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

1,2

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..21.

Eric Weisstein's World of Mathematics, Hex Number.

Eric Weisstein's World of Mathematics, Equilateral Triangle.

Example

For n = 2 the two kinds of non-congruent equilateral triangles are the following:
/. *     * .
. * *   . . *
\. .     * .

Crossrefs

Cf. A008893.

Sequence in context: A081689 A231559 A104813 * A039745 A298872 A298875

Adjacent sequences: A239695 A239696 A239697 * A239699 A239700 A239701

Keyword

nonn,more

Author

Martin Renner, Apr 17 2014

Extensions

a(7) from Martin Renner, May 31 2014

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

Status

approved