a(n) = 6^n + 6*n.

Terms

a(0) =1a(1) =12a(2) =48a(3) =234a(4) =1320a(5) =7806a(6) =46692a(7) =279978a(8) =1679664a(9) =10077750a(10) =60466236a(11) =362797122a(12) =2176782408a(13) =13060694094a(14) =78364164180a(15) =470184984666