A241228 - OEIS

%I #11 May 31 2014 10:39:55

%S 0,20,252,1296,4232,10668,22956,43832,77160,126972,198176,296976,

%T 429252,602876,825552,1106376,1454192,1879956,2397024,3014312,3747564,

%U 4609476

%N Number of 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/IsoscelesTriangle.html">Isosceles Triangle</a>.

%F a(n) = A241223(n) - A241227(n).

%Y Cf. A186434.

%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