A177288 Number of permutations of 2 copies of 1..n with all adjacent differences <= 7 in absolute value.

1, 1, 6, 90, 2520, 113400, 7484400, 681080400, 81729648000, 7580424852000, 569159625434400, 36636506215016400, 2141931687266957040

Offset: 0

Author

R. H. Hardin, May 06 2010

Keywords

• nonn
• more

Crossrefs

Cf. A000680.

Formula

a(n) = (2n)!/2^n for n<=8.

Extensions

a(0), a(12) from Alois P. Heinz, May 30 2025