A271614 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 5 elements linked to themselves.

1, 4, 26, 307, 7764, 222936, 3243689, 132728354, 30892003921, 3065366376540, 74672717363118, 12952235029243936, 25923218026065797712, 11188107558636007931696, 695394278635888843298780, 579704015638436450676621584, 9319830273030294425399538816052

Offset

1,2

Comments

Column 5 of A271617.

Links

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

Formula

a(n) = Sum_{i=0..2} A288852(n,floor(n*(n+1)/4)-i). - Alois P. Heinz, Jun 18 2017

Example

Some solutions for n=4
.....5........0........6........0........0........0........5........5
....2.0......0.0......0.1......4.3......4.3......0.5......2.5......2.0
...4.3.5....4.3.5....0.4.3....4.3.6....0.4.3....0.2.5....5.2.5....0.0.6
..0.0.2.0..4.3.2.0..0.4.3.0..0.0.0.1..0.0.4.3..4.3.2.0..2.0.2.0..0.4.3.1
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: A357795 A102202 A271613 * A136503 A114125 A063182

Adjacent sequences: A271611 A271612 A271613 * A271615 A271616 A271617

Keyword

nonn

Author

R. H. Hardin, Apr 10 2016

Extensions

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

Status

approved