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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. 0
1, 3, 17, 307, 7764, 222936, 18314708, 5436984025, 1549076843600, 327785587238680, 258598550473174218, 937062960563484014011, 2266270598091075686029983, 2979993347333205027776950744, 18769591152933109773812486076631, 672356922734153057389479052479321305 (list; graph; refs; listen; history; text; internal format)
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: A267658 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

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Last modified June 17 22:14 EDT 2021. Contains 345086 sequences. (Running on oeis4.)