Determine the number of permutations (p₁, p₂,...p₇) of 1,2, ...7; such that for all k 1≤k≤6, (p₁, p₂,... p_k) is not a permutation of (1,2, ...k); i.e., p₁≠1; (p₁, p₂) is not a permutation of (1,2), etc.

What would be the answer if we specify 1≤k<6 instead?

(In reply to solution? by bumble)

Nope; the permutation (1,2,3,4,5,7,6) doesn't have 7 at the last position, but doesn't fulfill the other conditions.

Posted by Old Original Oskar! on 2006-09-21 13:10:13