Number of 1 up, 1 down, 2 up, 1 down, 3 up, 1 down, ... permutations of [n].

A247550

Number of 1 up, 1 down, 2 up, 1 down, 3 up, 1 down, ... permutations of [n].

Terms

    a(0) =1a(1) =1a(2) =1a(3) =2a(4) =5a(5) =9a(6) =40a(7) =169a(8) =477a(9) =1099a(10) =8766a(11) =56341a(12) =234717a(13) =774279a(14) =2182270a(15) =27260478a(16) =249339033a(17) =1457282467a(18) =6624389780a(19) =25274016620a(20) =84400336507

External references