A271616 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 7 elements linked to themselves.

1, 4, 27, 406, 12180, 550173, 18314708, 1182352612, 291282493174, 42207024086536, 2070868688611599, 493143363040812884, 933291694075331622647, 530152639533410371743176, 60230981411511158858617306, 63827420909748305015725846472, 911985479463119474886614252798296

Offset

1,2

Comments

Column 7 of A271617.

Links

Table of n, a(n) for n=1..17.

Formula

a(n) = Sum_{i=0..3} A288852(n,floor(n*(n+1)/4)-i). - Alois P. Heinz, Jun 18 2017

Example

Some solutions for n=4
.....6........6........0........0........0........6........0........5
....0.1......6.1......4.3......4.3......0.6......0.1......0.5......2.5
...5.6.0....6.1.0....0.6.6....0.6.0....0.0.1....4.3.0....5.2.6....0.2.5
..2.0.1.0..0.1.4.3..4.3.1.1..0.0.1.0..4.3.4.3..0.4.3.0..2.0.0.1..0.0.2.0
Element moves: 0=itself 1=nw 2=ne 3=w 4=e 5=sw 6=se, reciprocals total 7

Crossrefs

Cf. A271617, A288852.

Sequence in context: A104169 A359904 A271615 * A123672 A269869 A119030

Adjacent sequences: A271613 A271614 A271615 * A271617 A271618 A271619

Keyword

nonn

Author

R. H. Hardin, Apr 10 2016

Extensions

a(14)-a(17) from Alois P. Heinz, Jun 15 2017

Status

approved