The number of permutations of {1,2,...,n,1,2,...,n} with the property that there are k numbers between the two k's in the set for k=1,...,n.
A176127
The number of permutations of {1,2,...,n,1,2,...,n} with the property that there are k numbers between the two k's in the set for k=1,...,n.
Terms
- a(0) =0a(1) =0a(2) =2a(3) =2a(4) =0a(5) =0a(6) =52a(7) =300a(8) =0a(9) =0a(10) =35584a(11) =216288a(12) =0a(13) =0a(14) =79619280a(15) =653443600a(16) =0a(17) =0a(18) =513629782560a(20) =0a(21) =0a(24) =0a(25) =0a(28) =0a(29) =0
External references
- oeis: A176127