Number of collinear triples in a 3 X n rectangular grid.

Terms

a(0) =0a(1) =1a(2) =2a(3) =8a(4) =20a(5) =43a(6) =78a(7) =130a(8) =200a(9) =293a(10) =410a(11) =556a(12) =732a(13) =943a(14) =1190a(15) =1478a(16) =1808a(17) =2185a(18) =2610a(19) =3088a(20) =3620a(21) =4211a(22) =4862a(23) =5578a(24) =6360a(25) =7213a(26) =8138a(27) =9140a(28) =10220a(29) =11383