a(n) = 4^n * (4*n)! / (n! * (4!)^n).A386759a(n) = 4^n * (4*n)! / (n! * (4!)^n).Terms a(0) =1a(1) =4a(2) =560a(3) =369600a(4) =672672000External referencesoeis: A386759