a(n) = 6*5^n-1.

Terms

a(0) =5a(1) =29a(2) =149a(3) =749a(4) =3749a(5) =18749a(6) =93749a(7) =468749a(8) =2343749a(9) =11718749a(10) =58593749a(11) =292968749a(12) =1464843749a(13) =7324218749a(14) =36621093749a(15) =183105468749a(16) =915527343749