A271609 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 n elements linked to themselves.

1, 3, 17, 307, 7764, 222936, 18314708, 5436984025, 1549076843600, 327785587238680, 258598550473174218, 937062960563484014011, 2266270598091075686029983, 2979993347333205027776950744, 18769591152933109773812486076631, 672356922734153057389479052479321305

Offset

1,2

Comments

Diagonal of A271617.

Links

Table of n, a(n) for n=1..16.

Example

Some solutions for n=4
.....6........0........0........6........6........0........0........0
....6.1......6.0......0.6......0.1......6.1......0.5......4.3......4.3
...5.1.6....0.1.6....4.3.1....0.6.6....5.1.6....0.2.6....0.0.6....5.6.0
..2.4.3.1..4.3.0.1..0.4.3.0..0.0.1.1..2.0.0.1..4.3.0.1..4.3.0.1..2.0.1.0
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: A374315 A155201 A062622 * A290806 A009592 A051294

Adjacent sequences: A271606 A271607 A271608 * A271610 A271611 A271612

Keyword

nonn

Author

R. H. Hardin, Apr 10 2016

Extensions

a(13)-a(16) from Alois P. Heinz, Jun 15 2017

Status

approved