3p^2 where p runs through the primes.

Terms

a(0) =12a(1) =27a(2) =75a(3) =147a(4) =363a(5) =507a(6) =867a(7) =1083a(8) =1587a(9) =2523a(10) =2883a(11) =4107a(12) =5043a(13) =5547a(14) =6627a(15) =8427a(16) =10443a(17) =11163a(18) =13467a(19) =15123a(20) =15987a(21) =18723a(22) =20667a(23) =23763a(24) =28227a(25) =30603a(26) =31827a(27) =34347a(28) =35643a(29) =38307