OFFSET
0,4
LINKS
Colin Defant and Kai Zheng, Stack-sorting with consecutive-pattern-avoiding stacks, arXiv:2008.12297 [math.CO], 2020.
EXAMPLE
The consecutive-123-avoiding stack-sorting map acts on permutations of length 3 by reversing every permutation except 321, which gets sent to 213. The permutation 213 has 2 preimages under this map (namely, 312 and 321), and every other permutation of length 3 has at most one preimage. Hence, a(3)=2.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Colin Defant, Aug 29 2020
STATUS
approved