Conjectured enumeration formulas for affine permutations avoiding patterns in S4S_4

Let fnpf_n^p denote the number of affine permutations of size nn that avoid the pattern pp. The patterns under consideration are 31423142, 34123412, and 41234123.

Enumeration conjecture. The following equalities hold:

fn3142=k=0n1nkn(n1+kk)2kf^{3142}_n=\sum_{k=0}^{n-1}\frac{n-k}{n}\binom{n-1+k}{k}2^k

and

fn3412=fn4123=13k=0n(nk)2(2kk).f^{3412}_n=f^{4123}_n=\frac{1}{3}\sum_{k=0}^n\binom{n}{k}^2\binom{2k}{k}.

These formulas give the conjectured enumeration of affine pattern-avoiding permutations for the three remaining patterns in S4S_4; the source provides no proof or resolution beyond initial calculations.

Sources & referencesView supporting material

Primary source

Andrew Crites, “Enumerating pattern avoidance for affine permutations”, arXiv:1002.1933 (2010).

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