55107190151domain: NAppears in sequencesThe game of Mousetrap with n cards (given n letters and n envelopes, how many ways are there to fill the envelopes so that at least one letter goes into its right envelope?).at n=14A002467Number of permutations p of [2n] having at least one index i with |p(i)-i| = n.at n=7A306675