The number of permutations of length n that can be sorted by 2 pop stacks in parallel.

A164870

The number of permutations of length n that can be sorted by 2 pop stacks in parallel.

Terms

    a(0) =1a(1) =2a(2) =6a(3) =22a(4) =84a(5) =320a(6) =1212a(7) =4576a(8) =17256a(9) =65048a(10) =245184a(11) =924160a(12) =3483408a(13) =13129952a(14) =49490592a(15) =186544480a(16) =703140672a(17) =2650342784a(18) =9989916864a(19) =37654917376a(20) =141932392320a(21) =534984681344

External references