a(n) = 4*binomial(9*n+4,n)/(9*n+4).

A234507

a(n) = 4*binomial(9*n+4,n)/(9*n+4).

Terms

    a(0) =1a(1) =4a(2) =42a(3) =580a(4) =9139a(5) =155664a(6) =2791404a(7) =51919296a(8) =992414925a(9) =19375620264a(10) =384734333698

External references