Number of non-equivalent ways to choose three points in an equilateral triangle grid of side n.

Terms

a(0) =0a(1) =1a(2) =6a(3) =25a(4) =87a(5) =238a(6) =575a(7) =1228a(8) =2425a(9) =4446a(10) =7734a(11) =12806a(12) =20422a(13) =31444a(14) =47072a(15) =68639a(16) =97929a(17) =136893a(18) =188061a(19) =254170a(20) =338679a(21) =445297a(22) =578616a(23) =743524a(24) =945968a(25) =1192243a(26) =1489894a(27) =1846869a(28) =2272575a(29) =2776880