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

A375223

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

Terms

    a(0) =1a(1) =1a(2) =16a(3) =327a(4) =11756a(5) =644315a(6) =50094570a(7) =5245258879a(8) =711662648968

External references