Hmmmm

5! is called five factorial and = 5 x 4 x 3 x 2 x1 = 120.

Factorial numbers really come into their own with combinations and permutations

6,9,1 is a combination while 6,9,1 and 9,6,1 and 1,6,9 and 1,9,6 are permutations


Sometimes a + b is not equal to b + a but only in fairly higher mathematics, tensors etc. Direction very important.