a(n) = n + floor( n^2/2 + n^3/3 ).

Terms

a(0) =0a(1) =1a(2) =6a(3) =16a(4) =33a(5) =59a(6) =96a(7) =145a(8) =210a(9) =292a(10) =393a(11) =515a(12) =660a(13) =829a(14) =1026a(15) =1252a(16) =1509a(17) =1799a(18) =2124a(19) =2485a(20) =2886a(21) =3328a(22) =3813a(23) =4343a(24) =4920a(25) =5545a(26) =6222a(27) =6952a(28) =7737a(29) =8579