234 letters
... that Leonhard Euler wrote 234 letters between 1760 and 1762 to Friederike Charlotte of Brandenburg-Schwedt?
... that <a href="./Leonhard_Euler" id="mwCIw" rel="mw:WikiLink" title="Leonhard Euler">Leonhard Euler</a> wrote <b id="mwCI0"><a href="./Letters_to_a_German_Princess" id="mwCI4" rel="mw:WikiLink" title="Letters to a German Princess">234 letters</a></b> between 1760 and 1762 to <a href="./Friederike_Charlotte_of_Brandenburg-Schwedt" id="mwCI8" rel="mw:WikiLink" title="Friederike Charlotte of Brandenburg-Schwedt">Friederike Charlotte of Brandenburg-Schwedt</a>?