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 A241230 Number of obtuse isosceles triangles on a centered hexagonal grid of size n. 2
 0, 12, 108, 528, 1674, 4104, 8622, 16206, 28332, 46200, 71484, 106746, 153552, 214860, 293166, 391470, 512592, 660546, 840840, 1054704, 1308696, 1606776 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 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. Eric Weisstein's World of Mathematics, Isosceles Triangle. FORMULA a(n) = A241228(n) - A241229(n). CROSSREFS Cf. A190318. Sequence in context: A271559 A154671 A321672 * A037972 A111990 A053469 Adjacent sequences:  A241227 A241228 A241229 * A241231 A241232 A241233 KEYWORD nonn,more AUTHOR Martin Renner, Apr 17 2014 EXTENSIONS a(7) from Martin Renner, May 31 2014 a(8)-a(22) from Giovanni Resta, May 31 2014 STATUS approved

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Last modified May 30 23:58 EDT 2020. Contains 334747 sequences. (Running on oeis4.)