Number of obtuse triangles on a centered hexagonal grid of size n.

Terms

a(0) =0a(1) =12a(2) =480a(3) =4488a(4) =22278a(5) =78288a(6) =220374a(7) =531594a(8) =1143648a(9) =2254440a(10) =4145244a(11) =7202190a(12) =11940444a(13) =19029300a(14) =29318754a(15) =43872402a(16) =63999528a(17) =91288794a(18) =127642164a(19) =175326336a(20) =237000816a(21) =315772032