A337522 - OEIS

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.

%I #9 Dec 21 2020 17:40:07

%S 1,1,2,5,15,50,179,675,2649,10734

%N 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.

%H C. Defant and K. Zheng, <a href="https://arxiv.org/abs/2008.12297">Stack-Sorting with Consecutive-Pattern-Avoiding Stacks</a>, arXiv:2008.12297 [math.CO], 2020.

%e 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.

%Y Cf. A033321, A001006, A337495, A011782, A001405

%K nonn,more

%O 0,3

%A _Colin Defant_, Aug 30 2020