Number of permutations of 1..n with no adjacent pair summing to n+2.
A173842
Number of permutations of 1..n with no adjacent pair summing to n+2.
Terms
- a(0) =1a(1) =1a(2) =2a(3) =2a(4) =12a(5) =48a(6) =336a(7) =1968a(8) =17760a(9) =140160a(10) =1543680a(11) =15298560a(12) =199019520a(13) =2373073920a(14) =35611269120a(15) =496199854080
External references
- oeis: A173842