A190310 - OEIS

%I #14 Feb 12 2024 06:51:17

%S 0,0,0,1,3,5,9,12,19,24,32,37,51,57,69,80,99,107,127,136,161,176,196,

%T 207,246,262,286,306,343,357,399,414,460,485,517,544,605,623,659,689,

%U 757

%N Number of obtuse isosceles triangles, distinct up to congruence, on an n X n grid (or geoboard).

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Geoboard.html">Geoboard</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) = A189978(n) - A190309(n) - A108279(n).

%Y Cf. A028419, A108279, A189978, A190022, A190309.

%K nonn

%O 1,5

%A _Martin Renner_, May 08 2011