A241228 Number of isosceles triangles on a centered hexagonal grid of size n.

0, 20, 252, 1296, 4232, 10668, 22956, 43832, 77160, 126972, 198176, 296976, 429252, 602876, 825552, 1106376, 1454192, 1879956, 2397024, 3014312, 3747564, 4609476

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, Isosceles Triangle.

Formula

a(n) = A241223(n) - A241227(n).

Crossrefs

Cf. A186434.

Sequence in context: A022744 A081143 A218101 * A306290 A075469 A028032

Adjacent sequences: A241225 A241226 A241227 * A241229 A241230 A241231

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