Number of permutations on [n] whose up-down signature has nonnegative partial sums and which have exactly two descents.

A321268

Number of permutations on [n] whose up-down signature has nonnegative partial sums and which have exactly two descents.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =0a(4) =22a(5) =172a(6) =856a(7) =3488a(8) =12746a(9) =43628a(10) =143244a(11) =457536a(12) =1434318a(13) =4438540a(14) =13611136a(15) =41473216a(16) =125797010a(17) =380341580a(18) =1147318004a(19) =3455325600a(20) =10394291094a(21) =31242645420a(22) =93853769320a(23) =281825553760a(24) =846030314842

External references