a(n) = n!/(7 * 20!).A157984a(n) = n!/(7 * 20!).Terms a(0) =3a(1) =66a(2) =1518a(3) =36432a(4) =910800a(5) =23680800a(6) =639381600a(7) =17902684800a(8) =519177859200External referencesoeis: A157984