a(n) = C(n+3,3)*n^3/4.

Terms

a(0) =0a(1) =1a(2) =20a(3) =135a(4) =560a(5) =1750a(6) =4536a(7) =10290a(8) =21120a(9) =40095a(10) =71500a(11) =121121a(12) =196560a(13) =307580a(14) =466480a(15) =688500a(16) =992256a(17) =1400205a(18) =1939140a(19) =2640715a(20) =3542000a(21) =4686066a(22) =6122600a(23) =7908550a(24) =10108800a(25) =12796875a(26) =16055676a(27) =19978245a(28) =24668560a(29) =30242360