a(n) = (2*(1 + n + (((10^n-1)/9) - n)/9)).

Terms

a(0) =2a(1) =4a(2) =8a(3) =32a(4) =256a(5) =2480a(6) =24704a(7) =246928a(8) =2469152a(9) =24691376a(10) =246913600a(11) =2469135824a(12) =24691358048a(13) =246913580272