a(n) = the number of permutations (p(1), p(2), ..., p(n)) of (1,2,...,n) where, for each k (2 <= k <= n), the sign of (p(k) - p(k-1)) equals the sign of (p(n+2-k) - p(n+1-k)).
A137782
a(n) = the number of permutations (p(1), p(2), ..., p(n)) of (1,2,...,n) where, for each k (2 <= k <= n), the sign of (p(k) - p(k-1)) equals the sign of (p(n+2-k) - p(n+1-k)).
Terms
- a(0) =1a(1) =1a(2) =2a(3) =2a(4) =12a(5) =24a(6) =200a(7) =540a(8) =6160a(9) =21616a(10) =306432a(11) =1310880a(12) =22338624a(13) =113017696a(14) =2245983168a(15) =13108918368a(16) =297761967360
External references
- oeis: A137782