Number of permutations p() of 1..n+2 with centered difference p(i+1)-p(i-1) < 0 exactly once.

A180879

Number of permutations p() of 1..n+2 with centered difference p(i+1)-p(i-1) < 0 exactly once.

Terms

    a(0) =3a(1) =12a(2) =50a(3) =160a(4) =525a(5) =1540a(6) =4662a(7) =13104a(8) =38346a(9) =105336a(10) =303732a(11) =823680a(12) =2361645a(13) =6357780a(14) =18208190a(15) =48814480a(16) =139952670a(17) =374315656a(18) =1075431084a(19) =2872519104a(20) =8273365282a(21) =22082137896a(22) =63760878300a(23) =170112213600a(24) =492371090100

External references