Factorial - dummies

By Mary Jane Sterling

Part of Finite Math For Dummies Cheat Sheet

The factorial operation says to multiply the designated number by every positive integer smaller than that number.

n! = n (n – 1) (n – 2) 3 2 1

When using the operation in the formulas for the number of permutations or combinations of n things taken k at a time, factorial values need to be inserted into the numerator and denominator of the fraction. The first sixteen factorial values are given here. And, by definition, 0! = 1.

n n! n n!
1 1 9 362,880
2 2 10 3,628,800
3 6 11 39,916,800
4 24 12 479,001,600
5 120 13 6,227,020,800
6 720 14 87,178,291,200
7 5,040 15 1,307,674,368,000
8 40,320 16 20,922,789,888,000