a(n) = 2*5^n - 3^n.

Terms

a(0) =1a(1) =7a(2) =41a(3) =223a(4) =1169a(5) =6007a(6) =30521a(7) =154063a(8) =774689a(9) =3886567a(10) =19472201a(11) =97479103a(12) =487749809a(13) =2439811927a(14) =12202248281a(15) =61020807343a(16) =305132734529