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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
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
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 18 2016
STATUS
approved

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Last modified July 16 15:16 EDT 2024. Contains 374349 sequences. (Running on oeis4.)