a(n) = 6^n + 6.

Terms

a(0) =7a(1) =12a(2) =42a(3) =222a(4) =1302a(5) =7782a(6) =46662a(7) =279942a(8) =1679622a(9) =10077702a(10) =60466182a(11) =362797062a(12) =2176782342a(13) =13060694022a(14) =78364164102a(15) =470184984582