A364819 Number of permutations p of [n] such that max(|p(p(i)) - i|)=1.

0, 0, 2, 6, 24, 80, 312, 1152, 4616, 18384, 77280, 328352, 1451712, 6527616, 30299504, 143322000, 696359232, 3448656512, 17483842176, 90301959744, 476270369600, 2557007766912, 13991998520832, 77867819879936, 441003737739264, 2537848321044480, 14843836828748672

Offset: 2

Author

Seiichi Manyama, Oct 21 2023

Keywords

• nonn

Crossrefs

Column k=1 of A364817.

Cf. A000085.

Formula

a(n) = Sum_{k=1..floor(n/4)} (n-2*k)! * A000085(n-4*k) / (k! * (n-4*k)!).