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 A241237 Number of isosceles triangles, distinct up to congruence, on a centered hexagonal grid of size n. 4
 0, 3, 15, 35, 69, 106, 162, 222, 300, 382, 486, 587, 715, 840, 997, 1147, 1313, 1491, 1700, 1890, 2129 (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, Isosceles Triangle. FORMULA a(n) = A241231(n) - A241236(n). EXAMPLE For n = 2 the three kinds of non-congruent isosceles triangles are the following: /. *     * *     * . . * *   . . *   . . * \. .     . .     * . CROSSREFS Cf. A189978, A241228. Sequence in context: A236693 A317183 A000466 * A145949 A015809 A293995 Adjacent sequences:  A241234 A241235 A241236 * A241238 A241239 A241240 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 January 22 19:16 EST 2020. Contains 331153 sequences. (Running on oeis4.)