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

0,3

Links

Table of n, a(n) for n=0..12.

Formula

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

Crossrefs

Cf. A000680.

Sequence in context: A177287 A177288 A177289 * A000680 A013297 A232979

Adjacent sequences: A177287 A177288 A177289 * A177291 A177292 A177293

Keyword

nonn,more

Author

R. H. Hardin, May 06 2010

Extensions

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

Status

approved