a(n) = (n-5)*(n-6)*(n-7)*(n-16)/24.

Terms

a(0) =-2a(1) =-7a(2) =-15a(3) =-25a(4) =-35a(5) =-42a(6) =-42a(7) =-30a(8) =0a(9) =55a(10) =143a(11) =273a(12) =455a(13) =700a(14) =1020a(15) =1428a(16) =1938a(17) =2565a(18) =3325a(19) =4235a(20) =5313a(21) =6578a(22) =8050a(23) =9750a(24) =11700a(25) =13923a(26) =16443a(27) =19285a(28) =22475a(29) =26040