a(n) = n*(n-1)*(n-2)*(n+3)/12.

Terms

a(0) =0a(1) =0a(2) =0a(3) =3a(4) =14a(5) =40a(6) =90a(7) =175a(8) =308a(9) =504a(10) =780a(11) =1155a(12) =1650a(13) =2288a(14) =3094a(15) =4095a(16) =5320a(17) =6800a(18) =8568a(19) =10659a(20) =13110a(21) =15960a(22) =19250a(23) =23023a(24) =27324a(25) =32200a(26) =37700a(27) =43875a(28) =50778a(29) =58464