a(n) = (9*n + 2)^2.

Terms

a(0) =4a(1) =121a(2) =400a(3) =841a(4) =1444a(5) =2209a(6) =3136a(7) =4225a(8) =5476a(9) =6889a(10) =8464a(11) =10201a(12) =12100a(13) =14161a(14) =16384a(15) =18769a(16) =21316a(17) =24025a(18) =26896a(19) =29929a(20) =33124a(21) =36481a(22) =40000a(23) =43681a(24) =47524a(25) =51529a(26) =55696a(27) =60025a(28) =64516a(29) =69169