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
Keywords
Links
- Andrew Howroyd, Table of n, a(n) for n = 0..200
Formula
a(n) = (2n)!/2^n for n<=4.
Extensions
a(0), a(13) from Alois P. Heinz, Jan 14 2016
Terms a(14) and beyond from Andrew Howroyd, May 14 2020