a(n) = Sum (J(p): p is a permutation of {1,2,...,n}), where J(p) is the number of j <= ceiling(n/2) such that p(j) + p(n+1-j) = n+1.

A155519

a(n) = Sum (J(p): p is a permutation of {1,2,...,n}), where J(p) is the number of j <= ceiling(n/2) such that p(j) + p(n+1-j) = n+1.

Terms

    a(0) =1a(1) =2a(2) =4a(3) =16a(4) =72a(5) =432a(6) =2880a(7) =23040a(8) =201600a(9) =2016000a(10) =21772800a(11) =261273600a(12) =3353011200a(13) =46942156800a(14) =697426329600

External references