A241237 Number of isosceles triangles, distinct up to congruence, on a centered hexagonal grid of size n.

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

Author

Martin Renner, Apr 17 2014

Keywords

• nonn

Comments

A centered hexagonal grid of size n is a grid with A003215(n-1) points forming a hexagonal lattice.

Examples

			For n = 2 the three kinds of non-congruent isosceles triangles are the following:
/. *     * *     * .
. * *   . . *   . . *
\. .     . .     * .
		

Links

• Eric Weisstein's World of Mathematics, Hex Number.
• Eric Weisstein's World of Mathematics, Isosceles Triangle.

Crossrefs

Cf. A189978, A241228.

Formula

a(n) = A241231(n) - A241236(n).

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