a(n) = 6^n + 7^n.

Terms

a(0) =2a(1) =13a(2) =85a(3) =559a(4) =3697a(5) =24583a(6) =164305a(7) =1103479a(8) =7444417a(9) =50431303a(10) =342941425a(11) =2340123799a(12) =16018069537a(13) =109949704423a(14) =756587236945