A177290 Number of permutations of 2 copies of 1..n with all adjacent differences <= 9 in absolute value.

1, 1, 6, 90, 2520, 113400, 7484400, 681080400, 81729648000, 12504636144000, 2375880867360000, 367786358267328000, 47683626117839712000

Offset: 0

Author

R. H. Hardin, May 06 2010

Keywords

• nonn
• more

Crossrefs

Cf. A000680.

Formula

a(n) = (2n)!/2^n for n<=10.

Extensions

a(0)=1 prepended and a(12) added by Alois P. Heinz, Jan 05 2022