3n^3 + 2n^2 + n + 1.

Terms

a(0) =1a(1) =7a(2) =35a(3) =103a(4) =229a(5) =431a(6) =727a(7) =1135a(8) =1673a(9) =2359a(10) =3211a(11) =4247a(12) =5485a(13) =6943a(14) =8639a(15) =10591a(16) =12817a(17) =15335a(18) =18163a(19) =21319a(20) =24821a(21) =28687a(22) =32935a(23) =37583a(24) =42649a(25) =48151a(26) =54107a(27) =60535a(28) =67453a(29) =74879