a(n) = 5^(n-1) * n! * Catalan(n-1).A221953a(n) = 5^(n-1) * n! * Catalan(n-1).Terms a(0) =1a(1) =10a(2) =300a(3) =15000a(4) =1050000a(5) =94500000a(6) =10395000000External referencesoeis: A221953