A271613 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 4 elements linked to themselves.

1, 4, 26, 307, 2571, 42702, 3243689, 132728354, 1491326272, 101843558868, 74672717363118, 12952235029243936, 334070494079203752, 109915013016304822208, 695394278635888843298780, 579704015638436450676621584, 44655320458467210977882177104, 75051772861714827753881814035744

Offset

1,2

Comments

Column 4 of A271617.

Links

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

Example

Some solutions for n=4
.....5........0........0........0........0........0........0........5
....2.0......4.3......0.0......6.0......0.0......4.3......6.6......2.6
...5.4.3....5.0.6....5.4.3....5.1.6....6.4.3....4.3.5....5.1.1....5.0.1
..2.4.3.0..2.4.3.1..2.0.4.3..2.4.3.1..0.1.4.3..4.3.2.0..2.4.3.0..2.4.3.0
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: A054592 A357795 A102202 * A271614 A136503 A114125

Adjacent sequences: A271610 A271611 A271612 * A271614 A271615 A271616

Keyword

nonn

Author

R. H. Hardin, Apr 10 2016

Extensions

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

Status

approved