For a non-negative integer n, n! = n × (n-1) × (n-2) × … × 1. By definition, 0! = 1.

Why is there a limit?

Factorials grow very fast. We limit input to avoid overflow (e.g. n ≤ 170 for approximate double precision).

Online Factorial Calculator

Calculate n! (n factorial) for non-negative integers. n! = n × (n-1) × … × 1; 0! = 1.

n (non-negative integer)

What is factorial?: For a non-negative integer n, n! = n × (n-1) × (n-2) × … × 1. By definition, 0! = 1.
Why is there a limit?: Factorials grow very fast. We limit input to avoid overflow (e.g. n ≤ 170 for approximate double precision).

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Calculate C(n,r) — the number of ways to choose r items from n without order. Uses n!/(r!(n-r)!).

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Calculate the number of ways to choose r items from n with repetition allowed. Formula: C(n+r-1, r).

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Count how many permutations of n objects are even (expressible as an even number of swaps). For n ≥ 2, equals n!/2.