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

Terms

a(0) =1a(1) =3a(2) =11a(3) =29a(4) =61a(5) =111a(6) =183a(7) =281a(8) =409a(9) =571a(10) =771a(11) =1013a(12) =1301a(13) =1639a(14) =2031a(15) =2481a(16) =2993a(17) =3571a(18) =4219a(19) =4941a(20) =5741a(21) =6623a(22) =7591a(23) =8649a(24) =9801a(25) =11051a(26) =12403a(27) =13861a(28) =15429a(29) =17111