Choose a type of number, then type an expression involving that number.
Number type:
Modulus:
Modulus:
p =
Input:
Result:
This program is a calculator that supports various different number systems besides the real numbers. For instance, it supports:
Not all operations are supported by all number systems (either due to the operation not making sense in that system, or due to me not having programmed it in yet). Some number systems may support additional operations.
Operation  Standard notation  Type as 

Addition  x + y  x + y

Subtraction  x  y  x  y

Multiplication  xy or x×y or x·y  x * y or xy

Division  x/y, x ÷ y  x / y

Exponents/powers  x^{y}  x ^ y

Exponents  e^{x}, exp x  exp x

Natural logarithms  ln x  ln x

Logarithms  log_{b} x  log_b x

Square roots  √x  sqrt x

Absolute value  x  x or abs x

Conjugate  x̄ or x^{*}  conj x

Ordinary counting numbers (1, 2, 3); may or may not include 0, depending on the specific definition. Does not include negative numbers, fractions, any sort of infinity, or imaginary numbers.
Cardinality: ℵ_{0}; structure: commutative monoid with both + and · (or a semigroup with + if 0 is not included); subset of: ℤ, ℚ, ℝ, ℂ
More information: Wikipedia
Operation  Standard notation  Type as  Properties 

Addition  x + y  x + y  closed, associative, commutative, has identity (0), no inverses 
Subtraction  x  y  x  y  partial, nonassociative, noncommutative, has right identity (0) 
Multiplication  xy or x×y or x·y  x * y  closed, associative, commutative, distributive over + and , has identity (1), possibly has absorbing element (0), no inverses 
Division  x/y, x ÷ y  x / y  partial (can't divide by 0, only some pairs of numbers are divisible), nonassociative, noncommutative, rightdistributive over + and , has right identity (1), possibly has left absorbing element (0) 
Exponents/powers  x^{y}  x ^ y  partial (y must be nonnegative), nonassociative, noncommutative, distributive over × and ÷, has right identity (1), has left absorbing element (0) 
Logarithms  log_{b} x  log_b x  
Square roots  √x  sqrt x  partial (not defined for x < 0, doesn't always give an integer), monotonically increasing, two fixed points (0, 1), onetoone 
GCD  gcd(x, y) or (x, y)  gcd(x, y) or (x, y)  closed, associative, commutative, has identity (0), has absorbing element (1), distributive over LCM 
LCM  lcm(x, y) or [x, y]  lcm(x, y) or [x, y]  closed, associative, commutative, has identity (1), has absorbing element (0), distributive over GCD 
Ordinary counting numbers (1, 2, 3) plus the negative numbers (1, 2, 3) and zero. Does not include fractions, any sort of infinity, or imaginary numbers.
Cardinality: ℵ_{0}; structure: integral domain; superset of: ℕ; subset of: ℚ, ℝ, ℂ
More information: Wikipedia
Operation  Standard notation  Type as  Properties 

Addition  x + y  x + y  closed, associative, commutative, has identity (0), has inverses (x) 
Subtraction  x  y  x  y  closed, nonassociative, noncommutative, has right identity (0) 
Multiplication  xy or x×y or x·y  x * y  closed, associative, commutative, distributive over + and , has identity (1), has absorbing element (0), no inverses 
Division  x/y, x ÷ y  x / y  partial (can't divide by 0, only some pairs of numbers are divisible), nonassociative, noncommutative, rightdistributive over + and , has right identity (1), has left absorbing element (0) 
Exponents/powers  x^{y}  x ^ y  partial (y must be nonnegative), nonassociative, noncommutative, distributive over × and ÷, has right identity (1) 
Logarithms  log_{b} x  log_b x  
Square roots  √x  sqrt x  partial (not defined for x < 0, doesn't always give an integer), monotonically increasing, two fixed points (0, 1), onetoone 
GCD  gcd(x, y) or (x, y)  gcd(x, y) or (x, y)  closed, associative, commutative, has identity (0), has absorbing element (1), distributive over LCM 
LCM  lcm(x, y) or [x, y]  lcm(x, y) or [x, y]  closed, associative, commutative, has identity (1), has absorbing element (0), distributive over GCD 
Absolute value  x  x or abs x  total, has fixed points (all nonnegative numbers), even 
The ordinary numbers we usually deal with. Includes irrational numbers (though this program can't represent irrational numbers exactly). Does not include any sort of infinity, or imaginary numbers.
Cardinality: ℶ_{1}; structure: field; superset of: ℕ, ℤ, ℚ; subset of: ℂ
More information: Wikipedia
Operation  Standard notation  Type as  Properties 

Addition  x + y  x + y  closed, associative, commutative, has identity (0), has inverses (x) 
Subtraction  x  y  x  y  closed, nonassociative, noncommutative, has right identity (0) 
Multiplication  xy or x×y or x·y  x * y  closed, associative, commutative, distributive over + and , has identity (1), has absorbing element (0), has inverses (1/x) 
Division  x/y, x ÷ y  x / y  partial (can't divide by 0), nonassociative, noncommutative, rightdistributive over + and , has right identity (1), has left absorbing element (0) 
Exponents/powers  x^{y}  x ^ y  partial (e.g. 1^{1/2} is undefined), nonassociative, noncommutative, distributive over × and ÷, has right identity (1) 
Exponents  e^{x}, exp x  exp x  total, monotonically increasing, no fixed points, onetoone 
Natural logarithms  ln x  ln x  partial (not defined for x ≤ 0), monotonically increasing, no fixed points, bijection (from domain where it's defined to ℝ) 
Logarithms  log_{b} x  log_b x  
Square roots  √x  sqrt x  partial (not defined for x < 0), monotonically increasing, two fixed points (0, 1), onetoone 
Includes all real numbers, and an imaginary unit i (sometimes written j instead) that's the square root of 1. Any complex number can be written as a + bi, where a and b are real numbers. Most operations behave similarly to the real numbers, with the notable exception that √xy ≠ √x·√y.
Cardinality: ℶ_{1}; structure: field; superset of: ℕ, ℤ, ℚ, ℝ
More information: Wikipedia
Operation  Standard notation  Type as  Properties 

Imaginary unit  i  i  
Addition  x + y  x + y  closed, associative, commutative, has identity (0), has inverses (x) 
Subtraction  x  y  x  y  closed, nonassociative, noncommutative, has right identity (0) 
Multiplication  xy or x×y or x·y  x * y or xy  closed, associative, commutative, distributive over + and , has identity (1), has inverses (1/x) 
Division  x/y, x ÷ y  x / y  partial (can't divide by 0), nonassociative, noncommutative, rightdistributive over + and , has right identity (1) 
Exponents/powers  x^{y}  x ^ y  nonassociative, noncommutative, has right identity (1) 
Exponents  e^{x}, exp x  exp x  total 
Natural logarithms  ln x  ln x  
Logarithms  log_{b} x  log_b x  
Square roots  √x  sqrt x  
Absolute value  x  x or abs x  total, has fixed points (all nonnegative real numbers) 
Conjugate  x̄ or x^{*}  conj x  total, has fixed points (all real numbers), bijection 
Splitcomplex numbers are like complex numbers, except instead of i there's j, which if you square it gives 1 rather than 1.
Cardinality: ℶ_{1}; structure: commutative ring; superset of: ℕ, ℤ, ℚ, ℝ
More info: Wikipedia
Operation  Standard notation  Type as  Properties 

Imaginary unit  j  j  
Addition  x + y  x + y  closed, associative, commutative, has identity (0), has inverses (x) 
Subtraction  x  y  x  y  closed, nonassociative, noncommutative, has right identity (0) 
Multiplication  xy or x×y or x·y  x * y or xy  closed, associative, commutative, distributive over + and , has identity (1) 
Division  x/y, x ÷ y  x / y  partial (can't divide by numbers of the form a ± aj), nonassociative, noncommutative, rightdistributive over + and , has right identity (1) 
Exponents/powers  x^{y}  x ^ y  nonassociative, noncommutative, has right identity (1) 
Exponents  e^{x}, exp x  exp x  
Natural logarithms  ln x  ln x  
Logarithms  log_{b} x  log_b x  
Square roots  √x  sqrt x  
Absolute value  x  x or abs x  total, has fixed points (all nonnegative real numbers) 
Conjugate  x̄ or x^{*}  conj x  total, has fixed points (all real numbers), bijection 
(I'm not sure if I got the power stuff right.)
Dual numbers are like complex numbers, except instead of i you have ε (epsilon; type this as ep
), and instead of ε^{2} being 1, it's 0.
This makes them kind of sort of like infinitesimals. Also, if you put in x + ε to a smooth function, then you get back both the result of the function at x (as the real part) and the derivative of the function at x (as the imaginary part).
Cardinality: ℶ_{1}; structure: commutative ring; superset of: ℕ, ℤ, ℚ, ℝ
More info: Wikipedia
Operation  Standard notation  Type as  Properties 

Imaginary unit  ε  epsilon or ep  
Addition  x + y  x + y  closed, associative, commutative, has identity (0), has inverses (x) 
Subtraction  x  y  x  y  closed, nonassociative, noncommutative, has right identity (0) 
Multiplication  xy or x×y or x·y  x * y or xy  closed, associative, commutative, distributive over + and , has identity (1) 
Division  x/y, x ÷ y  x / y  partial (can't divide by numbers whose real part is 0), nonassociative, noncommutative, rightdistributive over + and , has right identity (1) 
Exponents/powers  x^{y}  x ^ y  nonassociative, noncommutative, has right identity (1) 
Exponents  e^{x}, exp x  exp x  total 
Natural logarithms  ln x  ln x  
Logarithms  log_{b} x  log_b x  
Square roots  √x  sqrt x  
Conjugate  x̄ or x^{*}  conj x  total, has fixed points (all real numbers), bijection 
Similar to the complex numbers, except that there are three imaginary units, i, j, and k, all of which square to 1. Any quaternion can be written as a + bi + cj + dk, where a, b, c, and d are real numbers. Unlike complex numbers, multiplication is not commutative.
Cardinality: ℶ_{1}; structure: noncommutative ring; superset of: ℕ, ℤ, ℚ, ℝ, ℂ
More information: Wikipedia
Operation  Standard notation  Type as  Properties 

Imaginary units  i, j, k  i , j , k  
Addition  x + y  x + y  closed, associative, commutative, has identity (0), has inverses (x) 
Subtraction  x  y  x  y  closed, nonassociative, noncommutative, has right identity (0) 
Multiplication  xy or x×y or x·y  x * y or xy  closed, associative, noncommutative, has identity (1), has inverses (x^{1}) 
Exponents  e^{x}, exp x  exp x  total 
Natural logarithms  ln x  ln x  
Logarithms  log_{b} x  log_b x  
Square roots  √x  sqrt x  
Conjugate  x̄ or x^{*}  conj x  total, has fixed points (all real numbers), bijection 
This program does not yet support powers or division of quaternions
The extended real number line includes all real numbers, and two infinite numbers, ∞ and +∞. Unlike some other types of numbers, it does not include multiple sizes of infinity. The result of operations on infinite numbers generally depends on limits (like in calculus). Dividing by zero in the extended real numbers is still undefined; it is not infinity.
Cardinality: ℶ_{1}; superset of: ℕ, ℤ, ℚ, ℝ
More information: Wikipedia
Operation  Standard notation  Type as  Properties 

Addition  x + y  x + y  partial (∞ + ∞ undefined), associative, commutative, has identity (0), has inverses for finite numbers (x) 
Subtraction  x  y  x  y  partial, nonassociative, noncommutative, has right identity (0) 
Multiplication  xy or x×y or x·y  x * y  partial (∞·0 is undefined), associative, commutative, has identity (1), has inverses for finite nonzero numbers (1/x) 
Division  x/y, x ÷ y  x / y  partial (can't divide by 0, ∞/∞ is undefined), nonassociative, noncommutative, has right identity (1) 
Exponents/powers  x^{y}  x ^ y  nonassociative, noncommutative, has right identity (1) 
Exponents  e^{x}, exp x  exp x  total, fixed point (∞) 
Natural logarithms  ln x  ln x  partial (not defined for x < 0), fixed point (∞) 
Logarithms  log_{b} x  log_b x  
Square roots  √x  sqrt x  
Absolute value  x  x or abs x  total, has fixed points (all nonnegative numbers) 
Exponentiation info from Wikipedia: Exponentiation: Limits of powers and Wolfram MathWorld
The extended real number line includes all real numbers, and one infinity (∞). Not only does it not include multiple sizes of infinity, but it doesn't differentiate between positive and negative infinity; the number line can be thought of as a circle, with a single point at infinity, and positive numbers on one side of it, and negative numbers on the other side. Like the extended real number line, the result of operations on infinite numbers generally depends on limits (like in calculus). Unlike the extended real number line, dividing by zero is actually defined as infinity, except 0÷0, which is undefined.
Cardinality: ℶ_{1}; superset of: ℕ, ℤ, ℚ, ℝ
More information: Wikipedia
Operation  Standard notation  Type as  Properties 

Addition  x + y  x + y  Associative, commutative, has identity (0), has inverses for finite numbers (x), partial (∞ + ∞ undefined) 
Subtraction  x  y  x  y  Nonassociative, noncommutative, has right identity (0), partial 
Multiplication  xy or x×y or x·y  x * y  Associative, commutative, has identity (1), has inverses for finite nonzero numbers (1/x), partial (∞·0 is undefined) 
Division  x/y, x ÷ y  x / y  Nonassociative, noncommutative, has right identity (1), partial (0/0 and ∞/∞ are undefined) 
IEEE 754 is a standard for how computers can represent real numbers that aren't integers. Two main differences from real numbers:
There are also positive and negative zero.
Cardinality: 18437736874454810627 (= 2^{64}  2^{53} + 3)
More information: Wikipedia (and 64bit numbers in particular)
Operation  Standard notation  Type as  Properties 

Addition  x + y  x + y  Nonassociative, commutative, has identity (0; for numbers other than 0, 0 is also an identity), has inverses for finite numbers (x; only works for identity 0), closed 
Subtraction  x  y  x  y  Nonassociative, noncommutative, has right identity (0), closed 
Multiplication  xy or x×y or x·y  x * y  Nonassociative, commutative, has identity (1), has inverses for finite nonzero numbers (1/x), closed 
Division  x/y, x ÷ y  x / y  Nonassociative, noncommutative, has right identity (1), partial (can't divide by 0, ∞/∞ is undefined) 
Exponents/powers  x^{y}  x ^ y  Nonassociative, noncommutative, has right identity (1) 
Exponents  e^{x}, exp x  exp x  Closed, fixed point (∞) 
Natural logarithms  ln x  ln x  Closed, fixed point (∞) 
Logarithms  log_{b} x  log_b x  
Square roots  √x  sqrt x  
Absolute value  x  x or abs x  total, has fixed points (all nonnegative numbers and NaN) 
Cardinal numbers are a type of number used in set theory for describing the sizes of sets. Cardinal numbers include all the natural numbers (0, 1, 2, etc.) and also infinite numbers, the smallest of which is ℵ_{0} (which you can enter into this program by typing a0
), which represents the size of the set of natural numbers (sets with this cardinality are called countable). Negative numbers and fractions are not cardinal numbers, because sets can't have negative numbers or fracations of elements.
Many wellknown arguments showing things about sizes of infinity are about the cardinal numbers. Hilbert's hotel shows that a hotel with infinitely many guests can accomodate one more guest without any more rooms; this corresponds to the fact that ℵ_{0} + 1 = ℵ_{0}. The diagram here shows that the set of positive rationals (or the set of ordered pairs of natural numbers) is countable; this corresponds to the fact that ℵ_{0}^{2} = ℵ_{0}. Cantor's diagonal argument shows that the set of all real numbers, and also the set of all subsets of the natural numbers (called the power set of the natural numbers), are both uncountable; this corresponds to the fact that 2^{ℵ0} > ℵ_{0}.
What types of infinite cardinal numbers there are depends on which axioms of set theory you're using. This program uses ZermeloFraenkel set theory with the axiom of choice (ZFC), and assumes that the generalized continuum hypothesis is true.
Infinite cardinals in ZFC can be written as either ℵ_{n} (Hebrew letter aleph) or ℶ_{n} (Hebrew letter beth), where n is any ordinal number. The aleph numbers include all infinite cardinal numbers in order; that is, ℵ_{0} is the first infinite cardinal, ℵ_{1} is the second infinite cardinal, ℵ_{2} is the third infinite cardinal, etc. The beth numbers, on the other hand, only include infinite numbers that are 2 to the power of some other beth number [not quite true starting at ℶ_{ω}]; that is, ℶ_{0} = ℵ_{0}, ℶ_{1} = 2^{ℶ0}, ℶ_{2} = 2^{ℶ1}, etc. The generalized continuum hypothesis states that the aleph numbers and the beth numbers are the same.
No cardinality (proper class); superclass of: ℕ
More information: Wikipedia
Operation  Standard notation  Type as  Properties  Meaning 

Smallest infinite cardinal  ℵ_{0}  a0 or aleph_0  Size of ℕ  
Aleph numbers  ℵ_{x}  ax or aleph_x  xth cardinal number  
Beth numbers  ℶ_{x}  bx or beth_x  The size of the power set of the previous beth number  
Addition  x + y  x + y  Associative, commutative, has identity (0), no inverses, closed  The size of the union of two disjoint sets 
Subtraction  x  y  x  y  Nonassociative, noncommutative, has right identity (0), partial (not defined when x < y or when x and y are the same infinite cardinal)  Opposite of addition 
Multiplication  xy or x·y  x * y or xy  Associative, noncommutative, has identity (1), no inverses, closed  Size of a cross product 
Exponents/powers  x^{y}  x ^ y  Nonassociative, noncommutative, has right identity (1)  Size of the set of all functions from a set of size y to a set of size x 
Ordinal numbers are a type of number used in set theory for describing well orderings of sets. Ordinal numbers include all the natural numbers (0, 1, 2, etc., but not fractions like ½ or negative numbers like 1) and a lot of infinite numbers. (And by "a lot", I mean, there are more than any set, even infinite sets. Of course, this program can't handle all of them.) The smallest infinite ordinal is ω (which you can enter in this program by typing w
), and other infinite ordinals can be constructed by adding, multiplying, and using powers. Neither addition nor multiplication of ordinals is commutative.
There are also other ordinal numbers (such as ε_{0} and Γ_{0} and ω_{1}), but this program doesn't yet support them.
A well order is a total order—that is, for any two elements, one is less than the other, or they're equal—with the property that every nonempty subset has a least element. For instance, the usual way of ordering natural numbers (0, 1, 2, 3, ...) is a well order (any subset has a least element), but the usual way of ordering the integers (..., 3, 2, 1, 0, 1, 2, 3, ...) is not, because the set of all negative numbers has no least element, and neither is the usual ordering of nonnegative fractions, because the subset that contains only positive (nonzero) fractions has no smallest element. However, there are other ways of ordering these sets that are well orders; for instance, 0, 1, 2, 3, ..., 1, 2, 3, ... is a well order of the integers, and 0/1, 1/1, 2/1, ..., 1/2, 3/2, 5/2, ..., 1/3, 2/3, 4/3, 5/3, ..., ...... is a well order of the nonnegative rational numbers.
In any well order, both the positions of the elements and the size of the whole set can be described by ordinal numbers.
No cardinality (proper class); superclass of: ℕ
More information: Wikipedia
Operation  Standard notation  Type as  Properties 

Smallest infinite ordinal  ω  w or omega  
Addition  x + y  x + y  Associative, noncommutative, has identity (0), no inverses, closed 
Multiplication  xy or x·y  x * y or xy  Associative, noncommutative, has identity (1), no inverses, closed 
Exponents/powers  x^{y}  x ^ y  Nonassociative, noncommutative, has right identity (1) 
I had to figure out ordinal powers myself; I hope I did it right.
Like natural numbers, except that the prime factorization can have primes raised to infinity, and can have an infinite number of primes (though the latter isn't supported by this program). Addition and subtraction aren't defined for supernatural numbers, but multiplication and division are, as are greatest common divisor and least common multiple
More info: Wikipedia
Operation  Standard notation  Type as  Properties 

Infinity  ∞  inf  Only allowed in exponents (e.g., 2^inf )

Multiplication  xy or x×y or x·y  x * y  closed, associative, commutative, distributive over gcd and lcm, has identity (1), has absorbing element (∏p^{∞}), no inverses 
Division  x/y, x ÷ y  x / y  partial (only some pairs of numbers are divisible), nonassociative, noncommutative, has right identity (1), has left absorbing element (∏p^{∞}) 
Exponents/powers  x^{y}  x ^ y  y is an integer or ∞, nonassociative, noncommutative, has right identity (1), has left absorbing element (∏p^{∞}) 
GCD  gcd(x, y) or (x, y)  gcd(x, y) or (x, y)  closed, associative, commutative, has identity (0), has absorbing element (1), distributive over LCM 
LCM  lcm(x, y) or [x, y]  lcm(x, y) or [x, y]  closed, associative, commutative, has identity (1), has absorbing element (0), distributive over GCD 
The twoelement boolean algebra deals with truth values (0/false/no, 1/true/yes), with the operations "and" (represented as multiplication) and "or" (represented as addition). Unlike ordinary numbers, addition and multiplication distribute over each other. This differs from integers mod 2 in that + represents "or" here, but "xor" in integers mod 2.
Cardinality: 2; structure: boolean algebra (commutative monoid with both + and ·); subset of: ℕ (sort of)
More info: Wikipedia
Operation  Standard notation  Type as  Properties 

True  1 or ⊤  1  
False  0 or ⊥  0  
Or  x + y or x ∨ y  x + y  Associative, commutative, has identity (0), closed 
And  xy or x ∧ y  x * y  Associative, commutative, has identity (1), closed 
Not  ¬x or x̄  ~x  Closed 
Modular arithmetic deals with numbers that wrap around; that is, if you add some number n, you get back to where you started. Various things that can be represented with modular arithmetic:
Cardinality: n; structure: commutative ring, field if n is prime; subset of: ℕ (sort of)
More info: Wikipedia
Operation  Standard notation  Type as  Properties 

Addition  x + y  x + y  Associative, commutative, has identity (0), has inverses, closed 
Subtraction  x  y  x  y  Nonassociative, noncommutative, has right identity (0), closed 
Multiplication  xy or x×y or x·y  x * y or xy  Associative, commutative, has identity (1), has inverses for numbers coprime with n, closed 
Inverses  x^{1}  1 / x or  Partial 
Exponents/powers  x^{y}  x ^ y  Nonassociative, noncommutative, has right identity (1); y is not interpreted mod n 
Square roots  √x  sqrt x  Partial 
This is actually two things:
These groups are all isomorphic; that is, each element of the circle group corresponds to exactly one element of the reals mod n (for any n) and vice versa, and if you multiply two elements in the circle group, and you add their corresonding elements in the reals mod n, the result in the circle group corresponds to the result in the reals mod n. (Or, in other words, they can be thought of as the same group, just with different names for the elements and operations.)
More information: Wikipedia (circle group)
Cardinality: ℶ_{1}; structure: abelian group; subset of: ℝ (sort of, for reals mod n) or ℂ (for the circle group)
For reals mod n (additive group):
Operation  Standard notation  Type as  Properties 

Addition  x + y  x + y  closed, associative, commutative, has identity (0), has inverses (x) 
Subtraction  x  y  x  y  closed, nonassociative, noncommutative, has right identity (0) 
For the circle group:
Operation  Standard notation  Type as  Properties 

Element of the group  e^{xi}  e^(x*i) or exp(x*i)  
1, 1, i, i  1 , 1 , i , i  
Multiplication  xy or x×y or x·y  x * y  closed, associative, commutative, has identity (1), no absorbing element (0 is not part of the group), has inverses (1/x) 
Division  x/y, x ÷ y  x / y  closed, nonassociative, noncommutative, has right identity (1), no left absorbing element 
With normal real numbers, you can have numbers where the digits go on to the right of the decimal point infinitely (e.g., 3.333333… or 3.14159265…). padic numbers are similar, except you can have infinite digits to the left, so you can have numbers like …33333333. (There can still be a decimal point; however, there can only be finitely many digits to the right of it.)
What numbers you can have depends on the choice of base (the variable p represents the base), so a 2adic (i.e., base 2) number doesn't necessarily have a corresponding 3adic number; and a real number doesn't necessarily have a corresponding padic number, and vice versa. However, regardless of the base, all rational numbers can be represented.
Negative numbers can be represented as padic numbers without using a minus sign. For instance, 1 as a 10adic number is …999999, because if you add 1 to that, the last digit becomes 0, the 1 is carried, the next digit becomes 0, a 1 is carried again, and so on infinitely so all digits end up 0. In general, for any base p, negative integers start with an infinite number of p1 digits.
In padic numbers, numbers are considered to be close together if enough digits at the end of the number are the same.
Cardinality: ℶ_{1}; structure: field if p is prime, otherwise commutative ring; superset of: ℕ, ℤ, ℚ
More info: Wikipedia
Normally, prime bases are used. For this program, currently addition, subtraction, and multiplication work for all bases, but division and square root only work correctly for prime bases. For nonprime bases (that aren't powers of primes), you can get nonzero numbers that when multiplied together equal zero. Enter two coprime numbers that aren't 1 below to see an example of such numbers.
p = ×
If "interpret input as base p" is checked, you can enter digits higher than 10 by separating each digit with spaces or colons, or by using letters (like in hexadecimal). Also, quote notation is supported; that is, if you put an apostrophe in a number, everything to the left of the apostrophe will be repeated infinitely. If "interpret input as base p" is not checked, numbers you type will be treated as base 10 integers and converted to base p.
Operation  Standard notation  Type as  Properties  Notes 

Addition  x + y  x + y  Associative, commutative, has identity (…000), has inverses, closed  
Subtraction  x  y  x  y  Nonassociative, noncommutative, has right identity (…000), closed  
Multiplication  xy or x×y or x·y  x * y or xy  Associative, commutative, has identity (…001), has inverses if p is prime, closed  
Division  x/y, x ÷ y  x / y  Nonassociative, noncommutative, has right identity (1), partial (can't divide by 0)  This program assumes p is prime 
Square roots  √x  sqrt x  Partial (depends on last digit)  2adic square roots currently not supported; this program assumes p is prime 