a(n) = 10*7^n-1.

Terms

a(0) =9a(1) =69a(2) =489a(3) =3429a(4) =24009a(5) =168069a(6) =1176489a(7) =8235429a(8) =57648009a(9) =403536069a(10) =2824752489a(11) =19773267429a(12) =138412872009a(13) =968890104069