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A270510 Number of 2X2X2 triangular 0..n arrays with some element plus some adjacent element totalling n+1 exactly once. 1
3, 6, 21, 36, 63, 90, 129, 168, 219, 270, 333, 396, 471, 546, 633, 720, 819, 918, 1029, 1140, 1263, 1386, 1521, 1656, 1803, 1950, 2109, 2268, 2439, 2610, 2793, 2976, 3171, 3366, 3573, 3780, 3999, 4218, 4449, 4680, 4923, 5166, 5421, 5676, 5943, 6210, 6489 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row 2 of A270509.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = 2*a(n-1) -2*a(n-3) +a(n-4)

Empirical for n mod 2 = 0: a(n) = 3*n^2 - 3*n

Empirical for n mod 2 = 1: a(n) = 3*n^2 - 3*n + 3

EXAMPLE

Some solutions for n=4

...2....4....2....2....0....2....4....4....3....4....1....4....3....1....3....3

..3.4..2.3..4.3..3.1..4.1..1.4..3.1..1.2..4.2..2.1..2.4..3.2..4.1..0.4..2.4..2.0

CROSSREFS

Cf. A270509.

Sequence in context: A069558 A174461 A050611 * A300891 A056499 A056489

Adjacent sequences: A270507 A270508 A270509 * A270511 A270512 A270513

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 18 2016

STATUS

approved

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Last modified November 30 09:21 EST 2022. Contains 358438 sequences. (Running on oeis4.)