A151657 Number of permutations of 7 indistinguishable copies of 1..n with exactly 3 adjacent element pairs in decreasing order.

0, 1225, 818300, 160310458, 22727054364, 2892619063243, 354402440786800, 42837393111682484, 5153280785356119360, 618914057659003904189, 74290570601695876667092, 8915697686087571194412590, 1069916360274028756641650036, 128391238501628502906890984271

Offset

1,2

Links

Andrew Howroyd, Table of n, a(n) for n = 1..200

Formula

a(n) = 120^n - (7*n + 1)*36^n + binomial(7*n+1, 2)*8^n - binomial(7*n+1, 3). - Andrew Howroyd, May 07 2020

Prog

(PARI) a(n) = {120^n - (7*n + 1)*36^n + binomial(7*n+1, 2)*8^n - binomial(7*n+1, 3)} \\ Andrew Howroyd, May 07 2020

Crossrefs

Cf. A151625, A151656.

Sequence in context: A250848 A014795 A267297 * A218273 A046177 A031748

Adjacent sequences: A151654 A151655 A151656 * A151658 A151659 A151660

Keyword

nonn

Author

R. H. Hardin, May 29 2009

Extensions

Terms a(7) and beyond from Andrew Howroyd, May 07 2020

Status

approved