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

Terms

a(0) =2a(1) =1a(2) =0a(3) =5a(4) =26a(5) =77a(6) =176a(7) =345a(8) =610a(9) =1001a(10) =1552a(11) =2301a(12) =3290a(13) =4565a(14) =6176a(15) =8177a(16) =10626a(17) =13585a(18) =17120a(19) =21301a(20) =26202a(21) =31901a(22) =38480a(23) =46025a(24) =54626a(25) =64377a(26) =75376a(27) =87725a(28) =101530a(29) =116901