a(n) = (10^(2*n+1)-1)/3 + 6*10^n.

A332139

a(n) = (10^(2*n+1)-1)/3 + 6*10^n.

Terms

    a(0) =9a(1) =393a(2) =33933a(3) =3339333a(4) =333393333a(5) =33333933333

External references