A177291 Number of permutations of 3 copies of 1..n with all adjacent differences <= 1 in absolute value.

1, 1, 20, 92, 506, 2288, 10010, 41618, 168284, 664958, 2584442, 9916688, 37679618, 142079906, 532572428, 1987037318, 7386724082, 27381500624, 101272019258, 373902595130, 1378571667644, 5077289249390, 18683930010890, 68709775705328, 252549056389394, 927895845621746

Offset: 0

Author

R. H. Hardin, May 06 2010

Keywords

• nonn

Comments

a(n) = (3n)!/6^n = A014606(n) for n<=2.

Links

• Andrew Howroyd, Table of n, a(n) for n = 0..200

Crossrefs

Column k=3 of A331562.

Cf. A014606.

Extensions

a(0)=1 prepended by Alois P. Heinz, Jan 21 2020

a(19)-a(20) from Alois P. Heinz, Jan 22 2020

Terms a(21) and beyond from Andrew Howroyd, May 14 2020