@iq.psychology: If you solve this in 15 seconds, you are a genius. Factorial (n!) means multiplying a number by all the whole numbers below it down to 1. atmathlab Formula: n! = n x (n - 1) x (n - 2) x ... x 1 Examples: 5! = 5 x 4 x 3 x 2 x 1 = 120 4! = 4 x 3 x 2 x 1 = 24 3! = 3 x 2 x 1 = 6 Special case: 0! = 1 Simple meaning: Multiply all whole numbers from n down to 1. #iq #iqtest #mathmemes