a(n) = 8*11^n-1.

Terms

a(0) =7a(1) =87a(2) =967a(3) =10647a(4) =117127a(5) =1288407a(6) =14172487a(7) =155897367a(8) =1714871047a(9) =18863581527a(10) =207499396807