a(n) = 1/15*(128*n^5 + 320*n^4 + 80*n^3 - 200*n^2 + 92*n - 15).

Terms

a(0) =27a(1) =615a(2) =3843a(3) =14351a(4) =40363a(5) =94711a(6) =195859a(7) =368927a(8) =646715a(9) =1070727a(10) =1692195a(11) =2573103a(12) =3787211a(13) =5421079a(14) =7575091a(15) =10364479a(16) =13920347a(17) =18390695a(18) =23941443a(19) =30757455a(20) =39043563a(21) =49025591a(22) =60951379a(23) =75091807a(24) =91741819a(25) =111221447a(26) =133876835a(27) =160081263a(28) =190236171