A271611 Number of ways to reciprocally link elements of an n X n X n triangular array with themselves or a neighbor, with no more than 2 elements linked to themselves.

1, 3, 17, 114, 240, 2238, 216318, 5622392, 20454036, 970623228, 1038614548176, 131929454285752, 1257138602103744, 316487245419538728, 3147612978951707912144, 2069163709506683013857472, 63184698521304672890081520, 85953148896748583125564477008

Offset

1,2

Comments

Column 2 of A271617.

Links

Table of n, a(n) for n=1..18.

Example

Some solutions for n=4
.....6........5........0........0........5........5........0........5
....5.1......2.6......4.3......4.3......2.0......2.5......5.0......2.6
...2.0.0....5.0.1....5.5.0....5.4.3....6.4.3....5.2.5....2.4.3....4.3.1
..4.3.4.3..2.0.4.3..2.2.4.3..2.0.4.3..0.1.4.3..2.0.2.0..4.3.4.3..0.0.4.3
Element moves: 0=itself 1=nw 2=ne 3=w 4=e 5=sw 6=se, reciprocals total 7

Crossrefs

Cf. A271617.

Sequence in context: A119259 A249921 A174404 * A112111 A365856 A074554

Adjacent sequences: A271608 A271609 A271610 * A271612 A271613 A271614

Keyword

nonn

Author

R. H. Hardin, Apr 10 2016

Extensions

a(15)-a(18) from Alois P. Heinz, Jun 15 2017

Status

approved