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 A241233 Number of right triangles, distinct up to congruence, on a centered hexagonal grid of size n. 3
 0, 1, 5, 13, 25, 42, 62, 86, 115, 150, 191, 234, 282, 334, 395, 455, 526, 601, 677, 762, 855, 947, 1045, 1152, 1261, 1378, 1498, 1619, 1757, 1900, 2041, 2176, 2334, 2507, 2661, 2838, 3011, 3174, 3379, 3577, 3773, 3967, 4179, 4389, 4618, 4848, 5090, 5311, 5559, 5792, 6068 (list; graph; refs; listen; history; text; internal format)
 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, Right Triangle. FORMULA a(n) = A241231(n) - A241232(n) - A241234(n). EXAMPLE For n = 2 the only kind of non-congruent right triangles is the following: /. * * . * \. . CROSSREFS Cf. A189979, A241225. Sequence in context: A098483 A147205 A146875 * A064276 A240001 A301685 Adjacent sequences: A241230 A241231 A241232 * A241234 A241235 A241236 KEYWORD nonn AUTHOR Martin Renner, Apr 17 2014 EXTENSIONS a(7) from Martin Renner, May 31 2014 a(8)-a(21) from Giovanni Resta, May 31 2014 More terms from Bert Dobbelaere, Oct 17 2022 STATUS approved

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Last modified February 8 15:28 EST 2023. Contains 360149 sequences. (Running on oeis4.)