A177284 Number of permutations of 2 copies of 1..n with all adjacent differences <= 3 in absolute value.

1, 1, 6, 90, 2520, 41580, 516180, 6068622, 76331906, 958679970, 11679900408, 138047313960, 1610654864328, 18649754961744, 214256589488616, 2439692058769566, 27562317214408488, 309367132582535226, 3453299423388485028, 38354816922190327314, 424048220090513056908

Offset

0,3

Comments

a(n) = (2n)!/2^n for n<=4.

Links

Andrew Howroyd, Table of n, a(n) for n = 0..200

Crossrefs

Cf. A000680, A177283.

Sequence in context: A177592 A177593 A132467 * A266735 A177564 A177565

Adjacent sequences: A177281 A177282 A177283 * A177285 A177286 A177287

Keyword

nonn

Author

R. H. Hardin, May 06 2010

Extensions

a(0), a(13) from Alois P. Heinz, Jan 14 2016

Terms a(14) and beyond from Andrew Howroyd, May 14 2020

Status

approved