a(n) = (1/3)*n^5 + (1/2)*n^4 + (1/6)*n^3.

Terms

a(0) =0a(1) =1a(2) =20a(3) =126a(4) =480a(5) =1375a(6) =3276a(7) =6860a(8) =13056a(9) =23085a(10) =38500a(11) =61226a(12) =93600a(13) =138411a(14) =198940a(15) =279000a(16) =382976a(17) =515865a(18) =683316a(19) =891670a(20) =1148000a(21) =1460151a(22) =1836780a(23) =2287396a(24) =2822400a(25) =3453125a(26) =4191876a(27) =5051970a(28) =6047776a(29) =7194755