A239698 Number of equilateral triangles, distinct up to congruence, on a centered hexagonal grid of size n.

0, 2, 6, 11, 18, 25, 35, 45, 56, 69, 83, 97, 115, 131, 150, 169, 189, 212, 234, 258, 284

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 two kinds of non-congruent equilateral triangles are the following:
/. *     * .
. * *   . . *
\. .     * .
		

Links

• Eric Weisstein's World of Mathematics, Hex Number.
• Eric Weisstein's World of Mathematics, Equilateral Triangle.

Crossrefs

Cf. A008893.

Extensions

a(7) from Martin Renner, May 31 2014

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