Sorry for my english.
First of all check the value of k: 0 < k < n. If False, then the result is n, otherwise -- use formulas.

I saw your recent topic, so maybe someone will answer MY Q here (haha).

Guys, help me to understand. I see 'n!!…! = n(n−k)(n−2k)…(n mod k)', between '-' sign and 'k' IS value here(which changes from 0...2...X . I used X, 'cause I dont know, TO WHICH number should this value change (of course 'k' or 'n'), tell me to which and why ? Actually, I think this task isn't formalized as shoud be(tell me if i'm wrong please).

Thanks, you're right about that ... so stupid.

Edited by author 06.05.2015 13:09