Number of distinct lines passing through exactly two points in a triangular grid of side n.

Terms

a(0) =0a(1) =0a(2) =3a(3) =6a(4) =18a(5) =39a(6) =81a(7) =141a(8) =237a(9) =369a(10) =561a(11) =801a(12) =1119a(13) =1521a(14) =2043a(15) =2667a(16) =3429a(17) =4329a(18) =5415a(19) =6675a(20) =8163a(21) =9879a(22) =11877a(23) =14127a(24) =16695a(25) =19593a(26) =22881a(27) =26523a(28) =30591a(29) =35085