Number of permutations of 1..n with no adjacent pair summing to n+3.

A173843

Number of permutations of 1..n with no adjacent pair summing to n+3.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =6a(4) =12a(5) =72a(6) =336a(7) =2640a(8) =17760a(9) =175680a(10) =1543680a(11) =18385920a(12) =199019520a(13) =2771112960a(14) =35611269120a(15) =567422392320

External references