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%I #11 May 31 2014 10:40:18
%S 0,12,108,528,1674,4104,8622,16206,28332,46200,71484,106746,153552,
%T 214860,293166,391470,512592,660546,840840,1054704,1308696,1606776
%N Number of obtuse isosceles 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/ObtuseTriangle.html">Obtuse Triangle</a>.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/IsoscelesTriangle.html">Isosceles Triangle</a>.
%F a(n) = A241228(n) - A241229(n).
%Y Cf. A190318.
%K nonn,more
%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