a(n) = n^4/2-5*n^3/2+21*n-30.

Terms

a(0) =0a(1) =6a(2) =22a(3) =75a(4) =204a(5) =460a(6) =906a(7) =1617a(8) =2680a(9) =4194a(10) =6270a(11) =9031a(12) =12612a(13) =17160a(14) =22834a(15) =29805a(16) =38256a(17) =48382a(18) =60390a(19) =74499a(20) =90940a(21) =109956a(22) =131802a(23) =156745a(24) =185064a(25) =217050a(26) =253006a(27) =293247a(28) =338100a(29) =387904