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

1,2

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.

Eric Weisstein's World of Mathematics, Isosceles Triangle.

Formula

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

Crossrefs

Cf. A190318.

Sequence in context: A271559 A154671 A321672 * A353047 A037972 A111990

Adjacent sequences: A241227 A241228 A241229 * A241231 A241232 A241233

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