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%I #17 Sep 19 2017 03:42:51
%S 0,32,900,7380,34676,118044,325872,775856,1653888,3237984,5923028,
%T 10249596,16938588,26924036,41393424,61830480,90059672,128293728,
%U 179185500,245889068,332107188,442162836,581060024,754545360,969196896,1232477192,1552824900
%N Number of triangles on a centered hexagonal grid of size n.
%C A centered hexagonal grid of size n is a grid with A003215(n-1) points forming a hexagonal lattice.
%H Andrew Howroyd, <a href="/A241223/b241223.txt">Table of n, a(n) for n = 1..200</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/HexNumber.html">Hex Number</a>.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Triangle.html">Triangle</a>.
%F a(n) = A240826(n) - A241222(n).
%F a(n) = A241224(n) + A241225(n) + A241226(n) = A241227(n) + A241228(n).
%e For n = 2 the 32 triangles are the following:
%e /. * * * * . . . . . . . . * * *
%e . * * . * . * * . * * . . * . . * * * . * . . .
%e \. . . . . . * . * * . * . . * .
%e -
%e /* . . . . * * . . * * * * . . *
%e * . . * . * . . . . . * . . * . . . * . * * . .
%e \. * * . * * . * * . . * . . * .
%e -
%e /* . . . * * * * * . . . . . . *
%e . . . * . * . . * * . . * . . * . . . . * . . *
%e \* * . * . . . . * . * * * * . *
%e -
%e /* . . * * . . . . . . * * . . *
%e . * * * * . . * . * * . . * * . * . . . * * . .
%e \. . . . * . . * * . . * * . . *
%Y Cf. A045996.
%K nonn
%O 1,2
%A _Martin Renner_, Apr 17 2014
%E a(7) from _Martin Renner_, May 31 2014
%E a(8)-a(22) from _Giovanni Resta_, May 31 2014
%E Terms a(23) and beyond from _Andrew Howroyd_, Sep 18 2017
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