Number of collinear point 7-tuples in an n X n X n cubical grid.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =193a(7) =2072a(8) =12048a(9) =50400a(10) =169950a(11) =490776a(12) =1261308a(13) =2949264a(14) =6403947a(15) =13033792a(16) =25196840a(17) =46452864a(18) =82463460a(19) =141145632a(20) =234641712a(21) =379035984