a(n) = floor ( n(n+1)(n+2)(n+3) / (n+(n+1)+(n+2)+(n+3)) ).

Terms

a(0) =0a(1) =2a(2) =8a(3) =20a(4) =38a(5) =64a(6) =100a(7) =148a(8) =208a(9) =282a(10) =373a(11) =480a(12) =606a(13) =753a(14) =921a(15) =1112a(16) =1328a(17) =1571a(18) =1841a(19) =2140a(20) =2471a(21) =2833a(22) =3229a(23) =3661a(24) =4129a(25) =4635a(26) =5182a(27) =5769a(28) =6399a(29) =7074