a(n) = 9*binomial(10*n+9,n)/(10*n+9).

A234573

a(n) = 9*binomial(10*n+9,n)/(10*n+9).

Terms

    a(0) =1a(1) =9a(2) =126a(3) =2109a(4) =38916a(5) =763686a(6) =15636192a(7) =330237765a(8) =7141879503a(9) =157366449604

External references