A177287 Number of permutations of 2 copies of 1..n with all adjacent differences <= 6 in absolute value.

1, 1, 6, 90, 2520, 113400, 7484400, 681080400, 46118872800, 2475822056400, 113874710498640, 4828589411913540

Offset: 0

Author

R. H. Hardin, May 06 2010

Keywords

• nonn
• more

Formula

a(n) = (2n)!/2^n for n<=7.

Extensions

a(0)=1 prepended by Alois P. Heinz, Jul 21 2018