Number of ways to select 3 or more collinear points from a 3 X n grid.

Terms

a(0) =1a(1) =2a(2) =8a(3) =23a(4) =61a(5) =144a(6) =322a(7) =689a(8) =1439a(9) =2954a(10) =6004a(11) =12123a(12) =24385a(13) =48932a(14) =98054a(15) =196325a(16) =392899a(17) =786078a(18) =1572472a(19) =3145295a(20) =6290981a(21) =12582392a(22) =25165258a(23) =50331033a(24) =100662631a(25) =201325874a(26) =402652412a(27) =805305539a(28) =1610611849a(29) =3221224524