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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, 2341, 2598, 2842, 3126, 3394, 3711, 3995, 4341, 4641, 5024, 5349, 5750, 6128, 6540, 6959, 7381, 7772, 8255, 8722, 9252, 9688, 10220, 10698, 11277, 11806, 12381, 12905
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
Sequence in context: A236693 A317183 A000466 * A338351 A145949 A015809
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