A241238 Number of acute isosceles triangles, distinct up to congruence, on a centered hexagonal grid of size n.

0, 2, 11, 25, 50, 76, 117, 161, 216, 276, 352, 422, 516, 606, 720, 826, 949, 1079, 1222, 1367, 1534

Offset

1,2

Comments

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

Links

Table of n, a(n) for n=1..21.

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: A012213 A012251 A084547 * 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