A241226 Number of obtuse triangles on a centered hexagonal grid of size n.

0, 12, 480, 4488, 22278, 78288, 220374, 531594, 1143648, 2254440, 4145244, 7202190, 11940444, 19029300, 29318754, 43872402, 63999528, 91288794, 127642164, 175326336, 237000816, 315772032

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.

Crossrefs

Cf. A190020.

Formula

a(n) = A241223(n) - A241224(n) - A241225(n).

Extensions

a(7) from Martin Renner, May 31 2014

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