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

Terms

a(0) =-1a(1) =5a(2) =17a(3) =35a(4) =59a(5) =89a(6) =125a(7) =167a(8) =215a(9) =269a(10) =329a(11) =395a(12) =467a(13) =545a(14) =629a(15) =719a(16) =815a(17) =917a(18) =1025a(19) =1139a(20) =1259a(21) =1385a(22) =1517a(23) =1655a(24) =1799a(25) =1949a(26) =2105a(27) =2267a(28) =2435a(29) =2609