The alternating-group derangement bound conjecture

Let G=AnG=A_n be a finite simple transitive permutation group with point stabiliser HH, and let δ(G)\delta(G) denote the proportion of derangements in the action.

Alternating-group derangement bound conjecture. The following hold:

δ(G)1345,\delta(G)\geqslant\frac{13}{45},

with equality if and only if G=A8G=A_8 and H=AGL3(2)H={\rm AGL}_3(2); and, if n9n\geqslant9,

δ(G)[n!/e]n!(1)n(n1)n!,\delta(G)\geqslant\frac{[n!/e]}{n!}-\frac{(-1)^n(n-1)}{n!},

with equality if and only if H=An1H=A_{n-1}.

The second assertion gives the proposed non-asymptotic formula for the natural action and would make 13/4513/45 the optimal lower-bound constant for alternating groups. The source presents these statements as a conjecture based on computations.

Sources & referencesView supporting material

Primary source

Timothy C. Burness and Marco Fusari, “On derangements in simple permutation groups”, arXiv:2409.01043 (2025).

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