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Consider the symmetric group $S_n$ and, for each $\sigma \in S_n$, let $f(\sigma)$ be the number of fixed points of $\sigma$. Now let $g$ be the permutation such that $g(i)=i+1$ for $i=1,...,n-1$ and $g(n)=1$. We can partition $S_n$ in $(n-1)!$ sets of the form $$\sigma _g = \{\sigma, \sigma \circ g , \sigma \circ g ^2 ,..., \sigma \circ g ^{n-1}\}$$ for all $\sigma \in S_n$ such that $\sigma(1)=1$. Let $$h(\sigma _g) = \max \{f(\pi) \mid \pi \in \sigma _g\}. $$ Show that the average of $h(\sigma _g)$ for all $\sigma \in S_n$ such that $\sigma(1)=1$ is $3$ if $n\rightarrow \infty$.

The only thing I can do is show that the average of $f(\sigma)$ is $1$ if $n\rightarrow \infty$ using the formulas in [1]. I also tried to adapt the approaches in [2], but with no success. At last, I attempted to rewrite the problem in terms of permutation matrices, where $f$ is the trace of the matrix and apply some properties, also without success.

EDIT: so, from Carl Schildkraut's comment and also [3], it seems that this value explodes (although very slowly) as $n\rightarrow \infty$, as it's most likely $$\left( \frac{\log(n)}{\log(\log(n))} \right)$$ asymptotically, because, in each set $\sigma_g$, the distribution of the number of fixed points likely is $n$ Poisson distributions, so the expected maximum, according to [3], should be like that. So this question is most likely wrong and this limit may well be unbounded.

[1] https://en.wikipedia.org/wiki/Rencontres_numbers

[2] Fixed points of permutation groups

[3] https://arxiv.org/pdf/0903.4373.pdf

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    But then $g(n-1)=0\notin{1,\dots,n}$, isn't it? –  Jun 11 '22 at 16:26
  • @fitzcarraldo, we apply $g$ to a set and its value must be at least 1, because this set always has a permutation that fixes at least the number 1. It's impossible for this set to contain only permutations that have no fixed point. – Pedro Vaz Pimenta Jun 11 '22 at 16:57
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    @fitzcarraldo I think $g$ is supposed to be the permutation mapping $i$ to the number in ${1,2,\dots,n}$ equivalent to $i+1$ modulo $n$, not the number in ${0,1,2,\dots,n-1}$. So $g(n-1)=n$, and $g(n)=1$. – Carl Schildkraut Jun 11 '22 at 17:01
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    Oh, now I see that I used the same letter $g$ in two ways. Edited. Sorry for that. – Pedro Vaz Pimenta Jun 11 '22 at 17:05
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    Are you sure of this result? I have a (rather poor) heuristic that suggests this average should grow like $\Theta(\frac{\log n}{\log\log n})$, and numerical experiments give that this average should increase in $n$ and is larger than $3$ for large-ish $n$. – Carl Schildkraut Jun 11 '22 at 17:23

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