A337522 Number of permutations of length n that are sorted to the identity by a consecutive-312-avoiding-stack followed by a classical-21-avoiding stack.
1, 1, 2, 5, 15, 50, 179, 675, 2649, 10734
Offset: 0
Examples
Sending the permutation 132 through a consecutive-312-avoiding stack results in 231, and a classical 21-avoiding stack then sends 231 to 213, which is not the identity 123. Applying this procedure to any permutation of length 3 other than 132 results in 123, so a(3)=5.
Links
- C. Defant and K. Zheng, Stack-Sorting with Consecutive-Pattern-Avoiding Stacks, arXiv:2008.12297 [math.CO], 2020.