a(n) = ((3*n)!/n!^2)*(Gamma(1+n/2)/Gamma(1+3n/2)).

A091527

a(n) = ((3*n)!/n!^2)*(Gamma(1+n/2)/Gamma(1+3n/2)).

Terms

    a(0) =1a(1) =4a(2) =30a(3) =256a(4) =2310a(5) =21504a(6) =204204a(7) =1966080a(8) =19122246a(9) =187432960a(10) =1848483780a(11) =18320719872a(12) =182327718300

External references