a(n) = (4*n)! / (n! * (2*n)!).A349468a(n) = (4*n)! / (n! * (2*n)!).Terms a(0) =1a(1) =12a(2) =840a(3) =110880a(4) =21621600a(5) =5587021440External referencesoeis: A349468