a(n) = 2*(10^n - 7).

Terms

a(0) =6a(1) =186a(2) =1986a(3) =19986a(4) =199986a(5) =1999986a(6) =19999986a(7) =199999986a(8) =1999999986a(9) =19999999986a(10) =199999999986