every even perfect number comes from a Mersenne prime
... that after Euclid proved that every Mersenne prime leads to an even perfect number, it took more than 2000 years before Leonhard Euler proved that every even perfect number comes from a Mersenne prime?
... that after <a href="./Euclid" id="mwOQ" rel="mw:WikiLink" title="Euclid">Euclid</a> proved that every <a href="./Mersenne_prime" id="mwOg" rel="mw:WikiLink" title="Mersenne prime">Mersenne prime</a> leads to an even <a href="./Perfect_number" id="mwOw" rel="mw:WikiLink" title="Perfect number">perfect number</a>, it took more than 2000 years before <a href="./Leonhard_Euler" id="mwPA" rel="mw:WikiLink" title="Leonhard Euler">Leonhard Euler</a> proved that <b id="mwPQ"><a href="./Euclid–Euler_theorem" id="mwPg" rel="mw:WikiLink" title="Euclid–Euler theorem">every even perfect number comes from a Mersenne prime</a></b>?