a(n) = (n^3 + 9*n + 14*n + 9)/3.

Terms

a(0) =3a(1) =11a(2) =21a(3) =35a(4) =55a(5) =83a(6) =121a(7) =171a(8) =235a(9) =315a(10) =413a(11) =531a(12) =671a(13) =835a(14) =1025a(15) =1243a(16) =1491a(17) =1771a(18) =2085a(19) =2435a(20) =2823a(21) =3251a(22) =3721a(23) =4235a(24) =4795a(25) =5403a(26) =6061a(27) =6771a(28) =7535a(29) =8355