A241239 Number of obtuse isosceles triangles, distinct up to congruence, on a centered hexagonal grid of size n.

0, 1, 4, 10, 19, 30, 45, 61, 84, 106, 134, 165, 199, 234, 277, 321, 364, 412, 478, 523, 595

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.

Examples

			For n = 2 the only kind of non-congruent obtuse isosceles triangles is the following:
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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. A190310, A241230.

Formula

a(n) = A241237(n) - A241238(n).

Extensions

a(7) from Martin Renner, May 31 2014

a(8)-a(21) from Giovanni Resta, May 31 2014