a(n) = (5*n^3+12*n^2+n+6)/6.

Terms

a(0) =1a(1) =4a(2) =16a(3) =42a(4) =87a(5) =156a(6) =254a(7) =386a(8) =557a(9) =772a(10) =1036a(11) =1354a(12) =1731a(13) =2172a(14) =2682a(15) =3266a(16) =3929a(17) =4676a(18) =5512a(19) =6442a(20) =7471a(21) =8604a(22) =9846a(23) =11202a(24) =12677a(25) =14276a(26) =16004a(27) =17866a(28) =19867a(29) =22012