a(n) = (n^4 + 16*n^3 + 65*n^2 + 26*n + 12)/12.

Terms

a(0) =1a(1) =10a(2) =39a(3) =99a(4) =203a(5) =366a(6) =605a(7) =939a(8) =1389a(9) =1978a(10) =2731a(11) =3675a(12) =4839a(13) =6254a(14) =7953a(15) =9971a(16) =12345a(17) =15114a(18) =18319a(19) =22003a(20) =26211a(21) =30990a(22) =36389a(23) =42459a(24) =49253a(25) =56826a(26) =65235a(27) =74539a(28) =84799a(29) =96078