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%I #14 May 31 2014 10:41:26
%S 0,2,11,25,50,76,117,161,216,276,352,422,516,606,720,826,949,1079,
%T 1222,1367,1534
%N Number of acute isosceles triangles, distinct up to congruence, 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/AcuteTriangle.html">Acute Triangle</a>.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/IsoscelesTriangle.html">Isosceles Triangle</a>.
%F a(n) = A241237(n) - A241239(n).
%e For n = 2 the two kinds of non-congruent acute isosceles triangles are the following:
%e /. * * .
%e . * * . . *
%e \. . * .
%Y Cf. A190309, A241229.
%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(21) from _Giovanni Resta_, May 31 2014
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