a(n) is the number of permutations of the multiset 1,1, 2,2, ..., n,n such that exactly one pair k,k stays at its initial locations 2k-1, 2k.

A375222

a(n) is the number of permutations of the multiset 1,1, 2,2, ..., n,n such that exactly one pair k,k stays at its initial locations 2k-1, 2k.

Terms

    a(0) =1a(1) =0a(2) =15a(3) =296a(4) =10965a(5) =609864a(6) =47880595a(7) =5047886640a(8) =688359502089

External references