A241230 Number of obtuse isosceles triangles on a centered hexagonal grid of size n.

0, 12, 108, 528, 1674, 4104, 8622, 16206, 28332, 46200, 71484, 106746, 153552, 214860, 293166, 391470, 512592, 660546, 840840, 1054704, 1308696, 1606776

Offset: 1

Author

Martin Renner, Apr 17 2014

Keywords

• nonn
• more

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

Crossrefs

Cf. A190318.

Formula

a(n) = A241228(n) - A241229(n).

Extensions

a(7) from Martin Renner, May 31 2014

a(8)-a(22) from Giovanni Resta, May 31 2014