a(n) = 324*n^2 - 18.

Terms

a(0) =306a(1) =1278a(2) =2898a(3) =5166a(4) =8082a(5) =11646a(6) =15858a(7) =20718a(8) =26226a(9) =32382a(10) =39186a(11) =46638a(12) =54738a(13) =63486a(14) =72882a(15) =82926a(16) =93618a(17) =104958a(18) =116946a(19) =129582a(20) =142866a(21) =156798a(22) =171378a(23) =186606a(24) =202482a(25) =219006a(26) =236178a(27) =253998a(28) =272466a(29) =291582