A241234 Number of obtuse triangles, distinct up to congruence, on a centered hexagonal grid of size n.

0, 1, 15, 72, 220, 528, 1076, 1965, 3314, 5254, 7954, 11589, 16306, 22349, 29939, 39305, 50738, 64462, 80775, 100096, 122602, 148748, 178834, 213268, 252439, 296857, 346878, 402778, 465346, 534966, 611966, 697143, 790749, 893638, 1006128, 1129134, 1262932, 1408116, 1565674

Offset: 1

Author

Martin Renner, Apr 17 2014

Keywords

• nonn

Comments

A centered hexagonal grid of size n is a grid with A003215(n-1) points forming a hexagonal lattice.

Examples

			For n = 2 the only kind of non-congruent obtuse triangles is the following:
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Links

• Eric Weisstein's World of Mathematics, Hex Number.
• Eric Weisstein's World of Mathematics, Obtuse Triangle.

Crossrefs

Cf. A190022, A241226.

Formula

a(n) = A241231(n) - A241232(n) - A241233(n)

Extensions

a(7) from Martin Renner, May 31 2014

a(8)-a(14) from Giovanni Resta, May 31 2014

More terms from Bert Dobbelaere, Oct 17 2022