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

Terms

a(0) =2a(1) =11a(2) =26a(3) =47a(4) =74a(5) =107a(6) =146a(7) =191a(8) =242a(9) =299a(10) =362a(11) =431a(12) =506a(13) =587a(14) =674a(15) =767a(16) =866a(17) =971a(18) =1082a(19) =1199a(20) =1322a(21) =1451a(22) =1586a(23) =1727a(24) =1874a(25) =2027a(26) =2186a(27) =2351a(28) =2522a(29) =2699