Number of permutations of [n] having exactly one doubledescent.

A274997

Number of permutations of [n] having exactly one doubledescent.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =1a(4) =6a(5) =41a(6) =274a(7) =2040a(8) =16346a(9) =143571a(10) =1365354a(11) =14056287a(12) =155638724a(13) =1847352720a(14) =23400880036a(15) =315270938501

External references