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
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