a(n) = 7^n+6^n-1.

Terms

a(0) =1a(1) =12a(2) =84a(3) =558a(4) =3696a(5) =24582a(6) =164304a(7) =1103478a(8) =7444416a(9) =50431302a(10) =342941424a(11) =2340123798a(12) =16018069536a(13) =109949704422a(14) =756587236944