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Number of acute isosceles triangles on a centered hexagonal grid of size n.
2

%I #12 May 31 2014 10:40:11

%S 0,8,144,768,2558,6564,14334,27626,48828,80772,126692,190230,275700,

%T 388016,532386,714906,941600,1219410,1556184,1959608,2438868,3002700

%N Number of acute 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/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) = A241228(n) - A241230(n).

%Y Cf. A190317.

%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