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

1,2

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..22.

Eric Weisstein's World of Mathematics, Hex Number.

Eric Weisstein's World of Mathematics, Obtuse Triangle.

Formula

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

Crossrefs

Cf. A190020.

Sequence in context: A178217 A262584 A350154 * A003749 A012395 A012687

Adjacent sequences: A241223 A241224 A241225 * A241227 A241228 A241229

Keyword

nonn,more

Author

Martin Renner, Apr 17 2014

Extensions

a(7) from Martin Renner, May 31 2014

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

Status

approved