a(n) = (9*11^n+1)/2.

Terms

a(0) =5a(1) =50a(2) =545a(3) =5990a(4) =65885a(5) =724730a(6) =7972025a(7) =87692270a(8) =964614965a(9) =10610764610a(10) =116718410705