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

Terms

a(0) =0a(1) =8a(2) =204a(3) =1788a(4) =8690a(5) =30360a(6) =85194a(7) =205394a(8) =441876a(9) =870912a(10) =1601708a(11) =2783574a(12) =4616220a(13) =7358312a(14) =11339430a(15) =16972182a(16) =24763604a(17) =35328426a(18) =49405944a(19) =67873484a(20) =91762128a(21) =122276784