About factorial calculator
The factorial of n, written n!, is the product of all whole numbers from 1 to n. It counts the ways to arrange n different items.
Examples
5! = 5 × 4 × 3 × 2 × 1 = 120, and 0! is defined as 1. Five people can sit in a row in 120 different orders.
Grows very fast
20! is already about 2.4 × 10¹⁸. The tool works up to 170!, the largest factorial a standard decimal number can hold.
A worked example
6! is 720 and 10! is 3,628,800. The number of ways to choose 2 people from 5 uses factorials too: 5! ÷ (2! × 3!) = 10. Four letters can be arranged in 4! = 24 orders.
Large results
Results from 21! upwards no longer fit in a standard 64-bit integer, so exact values need special handling. This tool works up to 170!, the largest factorial a standard decimal number can hold.
