a(n) = 3*(4*n)!/(n!*(n+1)!^3).A361033a(n) = 3*(4*n)!/(n!*(n+1)!^3).Terms a(0) =3a(1) =9a(2) =280a(3) =17325a(4) =1513512a(5) =162954792a(6) =20193091776External referencesoeis: A361033