Floor[n(n-1)(n-2)(n-3)/14].

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =8a(6) =25a(7) =60a(8) =120a(9) =216a(10) =360a(11) =565a(12) =848a(13) =1225a(14) =1716a(15) =2340a(16) =3120a(17) =4080a(18) =5245a(19) =6644a(20) =8305a(21) =10260a(22) =12540a(23) =15180a(24) =18216a(25) =21685a(26) =25628a(27) =30085a(28) =35100a(29) =40716