a(n) = (7*n^2 - 17*n + 12)/2.

Terms

a(0) =1a(1) =3a(2) =12a(3) =28a(4) =51a(5) =81a(6) =118a(7) =162a(8) =213a(9) =271a(10) =336a(11) =408a(12) =487a(13) =573a(14) =666a(15) =766a(16) =873a(17) =987a(18) =1108a(19) =1236a(20) =1371a(21) =1513a(22) =1662a(23) =1818a(24) =1981a(25) =2151a(26) =2328a(27) =2512a(28) =2703a(29) =2901