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 A241238 Number of acute isosceles triangles, distinct up to congruence, on a centered hexagonal grid of size n. 1
 0, 2, 11, 25, 50, 76, 117, 161, 216, 276, 352, 422, 516, 606, 720, 826, 949, 1079, 1222, 1367, 1534 (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. Eric Weisstein's World of Mathematics, Isosceles Triangle. FORMULA a(n) = A241237(n) - A241239(n). EXAMPLE For n = 2 the two kinds of non-congruent acute isosceles triangles are the following: /. *     * . . * *   . . * \. .     * . CROSSREFS Cf. A190309, A241229. Sequence in context: A009189 A012213 A012251 * A296285 A077482 A141428 Adjacent sequences:  A241235 A241236 A241237 * A241239 A241240 A241241 KEYWORD nonn,more 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 STATUS approved

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Last modified December 12 07:31 EST 2019. Contains 329948 sequences. (Running on oeis4.)