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

1,3

Comments

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

Links

Table of n, a(n) for n=1..39.

Eric Weisstein's World of Mathematics, Hex Number.

Eric Weisstein's World of Mathematics, Obtuse Triangle.

Formula

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

Example

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

Cf. A190022, A241226.

Sequence in context: A145053 A168298 A126274 * A212097 A212098 A053531

Adjacent sequences: A241231 A241232 A241233 * A241235 A241236 A241237

Keyword

nonn

Author

Martin Renner, Apr 17 2014

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

Status

approved