a(n) = 8^n - 7^n.

Terms

a(0) =0a(1) =1a(2) =15a(3) =169a(4) =1695a(5) =15961a(6) =144495a(7) =1273609a(8) =11012415a(9) =93864121a(10) =791266575a(11) =6612607849a(12) =54878189535a(13) =452866803481