OFFSET
0,5
COMMENTS
A permutation is parity-alternating if it sends odd integers to odd integers, and even integers to even integers. It avoids 123 if there is no subsequence a..b..c with a < b < c. The values are computed by Michael Albert, see MathOverflow link.
The odd-indexed entries agree with the odd-indexed entries in A354208. A bijection is given by reversing the permutation.
LINKS
Per Alexandersson, Samuel Asefa Fufa, Frether Getachew and Dun Qiu, Pattern-avoidance and Fuss-Catalan numbers, arXiv:2201.08168 [math.CO], 2022. See also J. Int. Seq. (2023) Vol. 26, Art. 23.4.2.
MathOverflow, 321-avoiding and parity-alternating permutations, Jun 06 2022.
EXAMPLE
For n=4, the three permutations are 3412, 3214, 1432.
For n=5, we have 54321, 52143, 32541.
For n=6, we have 563412, 563214, 543612, 543216, 561432, 541632, 365412, 365214, 321654, 165432.
CROSSREFS
KEYWORD
nonn
AUTHOR
Per W. Alexandersson, Jun 18 2022
STATUS
approved