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%I #10 May 31 2014 10:39:12
%S 0,12,216,1104,3708,9396,20304,38868,68364,112632,176076,263832,
%T 381924,536424,735240,985896,1296540,1676508,2137392,2689248,3344244,
%U 4114020
%N Number of right 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 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/RightTriangle.html">Right Triangle</a>.
%F a(n) = A241223(n) - A241224(n) - A241226(n).
%Y Cf. A077435.
%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
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