a(n) = 4*binomial(5*n,n)/(5*n-1).

Terms

a(0) =5a(1) =20a(2) =130a(3) =1020a(4) =8855a(5) =81900a(6) =791120a(7) =7887660a(8) =80560285a(9) =838553320a(10) =8863227100a(11) =94871786100