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 A241224 Number of acute triangles on a centered hexagonal grid of size n. 4
 0, 8, 204, 1788, 8690, 30360, 85194, 205394, 441876, 870912, 1601708, 2783574, 4616220, 7358312, 11339430, 16972182, 24763604, 35328426, 49405944, 67873484, 91762128, 122276784 (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, Acute Triangle. FORMULA a(n) = A241223(n) - A241225(n) - A241226(n). EXAMPLE For n = 2 the eight acute triangles are the following: /. *     * *     * .     . .     . .     . .     * .     . * . * *   . * .   * * .   * * .   . * .   . * *   . . *   * . . \. .     . .     . .     * .     * *     . *     * .     . * CROSSREFS Cf. A190019, A241223. Sequence in context: A264124 A317631 A309904 * A259065 A204247 A063856 Adjacent sequences:  A241221 A241222 A241223 * A241225 A241226 A241227 KEYWORD nonn 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 August 1 03:05 EDT 2021. Contains 346379 sequences. (Running on oeis4.)