Number of permutations of {1,2,3,...,n} each with the same up-down signature as its inverse permutation.

A135410

Number of permutations of {1,2,3,...,n} each with the same up-down signature as its inverse permutation.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =26a(6) =80a(7) =272a(8) =1076a(9) =4848a(10) =24832a(11) =142340a(12) =902440a(13) =6257264a(14) =47042924a(15) =380800060a(16) =3300070116a(17) =30472353884a(18) =298595442140

External references