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A241234
Number of obtuse triangles, distinct up to congruence, on a centered hexagonal grid of size n.
3
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
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
Sequence in context: A145053 A168298 A126274 * A212097 A212098 A053531
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