In an undergrad honors algebra course it's sometimes shown that when $p$ is prime and $>3$ then
$PSL_2(Z/p)$ is simple of of order $p(p-1)(p+1)/2$. But that this is the "only" simple group
having that order is seldom or never (except when $p=5$) proved.


I've worked out a fairly simple proof, using the Burnside transfer theorem, of this last
result, but it's perhaps a little too intricate to present in class.


QUESTION:  Are there proofs of this result, on-line or in texts, that are appropriate for
an undergrad honors algebra class? (If not, I might post an argument on arXiv).