A151577 Number of permutations of 1..n arranged in a circle with exactly 4 adjacent element pairs in decreasing order.

0, 5, 156, 2114, 19328, 140571, 882340, 5007112, 26441856, 132439905, 637468300, 2976161790, 13569454592, 60725449335, 267757190100, 1166662948900, 5034645823680, 21556696454685, 91704869986620, 388044105102650, 1634678955350400, 6860481786528275, 28700914012807556

Offset

4,2

Links

Andrew Howroyd, Table of n, a(n) for n = 4..500

Formula

From Andrew Howroyd, May 05 2020: (Start)

a(n) = n*A000498(n-1).

a(n) = n*(4^(n-1) - n*3^(n-1) + binomial(n,2)*2^(n-1) - binomial(n,3)). (End)

Prog

(PARI) a(n) = {n*(4^(n-1) - n*3^(n-1) + binomial(n, 2)*2^(n-1) - binomial(n, 3))} \\ Andrew Howroyd, May 05 2020

Crossrefs

Column k=4 of A334218.

Cf. A000498.

Sequence in context: A237527 A015019 A225165 * A032391 A139978 A304147

Adjacent sequences: A151574 A151575 A151576 * A151578 A151579 A151580

Keyword

nonn

Author

R. H. Hardin, May 21 2009

Extensions

Terms a(17) and beyond from Andrew Howroyd, May 05 2020

Status

approved