Problem. (1 Viewer)

[BIGTYMA]

Let

is permutaion of

. For this permutaion call the pair

wrong pair if

and

.Let number of inversion is number of wrong pair of permutation

. Let

is positive integer. Find the number of permutation of

such that its number of inversion is divisible by

.

somebody lend me a hand?

 

[Affinity]

(n-1)!

EDIT: here's a link http://www.mathlinks.ro/Forum/resources.php?p=1139336
it's a standard trick. Essentially what they aare saying is that for each permutation of the first n-1 elements, there is precisely 1 place where the nth can go to make the number og inversions a multiple of n