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A364819
Number of permutations p of [n] such that max(|p(p(i)) - i|)=1.
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
2,3
FORMULA
a(n) = Sum_{k=1..floor(n/4)} (n-2*k)! * A000085(n-4*k) / (k! * (n-4*k)!).
CROSSREFS
Column k=1 of A364817.
Cf. A000085.
Sequence in context: A372854 A275206 A095110 * A189858 A189568 A002742
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Oct 21 2023
STATUS
approved