a(n) = 5*9^n-1.

A198962

a(n) = 5*9^n-1.

Terms

    a(0) =4a(1) =44a(2) =404a(3) =3644a(4) =32804a(5) =295244a(6) =2657204a(7) =23914844a(8) =215233604a(9) =1937102444a(10) =17433922004a(11) =156905298044

External references