First post here. Tried to get the most minimalistic way to calculate the amount of permutations. The typical formula is:

n! = 1 * 2 * 3 ... * r * r + 1 * ... n
r! = 1 * 2 * 3 ... * r

But since every number between 1 and r is simplified, it's just a multiplication of the (x)range between r+1 and n.

Also as an example of lambda functions on python, and the reduce function, which takes every pair inside a list-type object and runs the function over them.