IMO 1986 LL GRE39

Let S be a k-element set.

imolonglistmathematicsolympiad

IMO 1986 LL GRE39

Origin: GRE

Problem

Let S be a k-element set. (a) Find the number of mappings f : S \toS such that (i) f(x) ̸= x for x \inS, (ii) f(f(x)) = x for x \inS. (b) The same with the condition (i) left out.