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There is a question regarding generation of finite simple groups with elements of prime order. Recently, Guralnick, Shareshian, Woodroofe and Teräväinen made advances in this direction. We have, for example, the following result:

Theorem. Assume that $n>7$. Let $p$ be a prime satisfying $n/2 < p < n-2$ and let $y \in A_n$ have order $p$. If $n$ is odd let $x \in A_n$ be an $n$-cycle. If $n$ is even let $x \in A_n$ be the product of two disjoint $\frac{n}{2}$-cycles. Then $x$ and $y$ generate $A_n$ invariably.

If we choose $n$ to be a prime, I think using the Prime Number Theorem we can get infinitely many pairs of primes $(n,p)$ satisfying the hypothesis of the Theorem so that we have infinitely many alternating groups generated by elements of prime order.

Now, if we have an infinite set of primes not necessarily having all primes this is not true. I mean, I think we can construct an infinite set of primes having no pairs satisfying the hypothesis of the Theorem.

Question. Given arbitrarily an infinite set of primes $\mathcal{P}$, can we choose some elements $x,y$ of orders $p,q \in \mathcal{P}$ such that $x$ and $y$ generates $A_n$ for some $n$?

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    $\begingroup$ In the question do you mean generates or invariably generates? The answer is positive in the former case and probably negative in the latter. $\endgroup$ Commented Nov 28 at 14:21
  • $\begingroup$ Invariably generators would be great, but I mean just generators. Do you know some argument to explain it (in the former case)? $\endgroup$
    – Lucas
    Commented Nov 28 at 14:32
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    $\begingroup$ Yes, I posted an answer. $\endgroup$ Commented Nov 28 at 15:12
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    $\begingroup$ There is no need to use the PNT; such a prime $p$ exists for every $n>7$ by Bertrand’s postulate. I’m pretty sure the authors intended to read it this way, and it’s the whole reason for the assumption $n>7$. $\endgroup$ Commented Nov 28 at 16:27
  • $\begingroup$ A possibly interesting variant of the question: Given an arbitrary infinite set of primes P, is there some N, so that for every n > N, A_n is generated by two elements with orders in P? $\endgroup$ Commented Dec 8 at 17:01

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For any two odd primes $p\le q$ there exist $x,y\in A_q$ of order $p,q$ respectively such that $A_q=\langle x,y\rangle$. First assume $p<q$ and take $x=(12\cdots p),y=(12\cdots q)$. Then $yxy^{-1}x^{-1}$ is a 3-cycle and by Jordan's theorem $\langle x,y\rangle$ is all of $A_q$. For $p=q$ take $x=(12\cdots p),\,y=(2134\cdots p)$ and note that $xy^{-1}$ is a 3-cycle.

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