

A241238


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


1



0, 2, 11, 25, 50, 76, 117, 161, 216, 276, 352, 422, 516, 606, 720, 826, 949, 1079, 1222, 1367, 1534
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OFFSET

1,2


COMMENTS

A centered hexagonal grid of size n is a grid with A003215(n1) 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, Acute Triangle.
Eric Weisstein's World of Mathematics, Isosceles Triangle.


FORMULA

a(n) = A241237(n)  A241239(n).


EXAMPLE

For n = 2 the two kinds of noncongruent acute isosceles triangles are the following:
/. * * .
. * * . . *
\. . * .


CROSSREFS

Cf. A190309, A241229.
Sequence in context: A009189 A012213 A012251 * A296285 A077482 A141428
Adjacent sequences: A241235 A241236 A241237 * A241239 A241240 A241241


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



