Product_{i=1..n} (i-1)!*(i+2*n-1)!/(i+n-1)!.A055968Product_{i=1..n} (i-1)!*(i+2*n-1)!/(i+n-1)!.Terms a(0) =1a(1) =2a(2) =240a(3) =16934400External referencesoeis: A055968