A177292 Number of permutations of 3 copies of 1..n with all adjacent differences <= 2 in absolute value.

1, 1, 20, 1680, 51240, 1173512, 31006978, 788946320, 18721725280, 435630242080, 9998202729808, 225310437716462

Offset: 0

Author

R. H. Hardin, May 06 2010

Keywords

• nonn

Comments

a(n) = (3n)!/6^n for n<=3.

Crossrefs

Cf. A014606.

Extensions

a(0) and a(11) from Alois P. Heinz, Jan 18 2016