(3n)!/[3n*n!*(n+1)!].A205824(3n)!/[3n*n!*(n+1)!].Terms a(0) =1a(1) =10a(2) =280a(3) =13860a(4) =1009008a(5) =98017920a(6) =11972188800External referencesoeis: A205824