a(n) = (2*n - 1)*(3*n + 1).

Terms

a(0) =-1a(1) =4a(2) =21a(3) =50a(4) =91a(5) =144a(6) =209a(7) =286a(8) =375a(9) =476a(10) =589a(11) =714a(12) =851a(13) =1000a(14) =1161a(15) =1334a(16) =1519a(17) =1716a(18) =1925a(19) =2146a(20) =2379a(21) =2624a(22) =2881a(23) =3150a(24) =3431a(25) =3724a(26) =4029a(27) =4346a(28) =4675a(29) =5016