a(n) = floor(C(n,6)/7).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =1a(8) =4a(9) =12a(10) =30a(11) =66a(12) =132a(13) =245a(14) =429a(15) =715a(16) =1144a(17) =1768a(18) =2652a(19) =3876a(20) =5537a(21) =7752a(22) =10659a(23) =14421a(24) =19228a(25) =25300a(26) =32890a(27) =42287a(28) =53820a(29) =67860