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A239698
Number of equilateral triangles, distinct up to congruence, on a centered hexagonal grid of size n.
0
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
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
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