Of the word ΕΙ engraven over the gate of Apollo's temple at Delphi (7)

Theon having ended his speech, I think it was Eustrophus the Athenian who said to us: Do you not see how valiantly Theon vindicates logic, having, in a manner, got on the lion’s skin? So it is not right even for us—who comprehensively place all the affairs, nature, and principles of things both divine and human in number, and make it most especially the author and lord of honest and estimable things—to be at quiet, but we must willingly offer the first-fruits of our dear mathematics to the God; since we think that this letter E does not of itself differ from the other letters either in power, figure, or expression, but that it has been preferred as being the sign of that great number which has an influence over all things, called the Quinary (or Pemptas), from which the Sages

have expressed the art of numbering by the verb πεμπτάζειν (signifying to account by fives). Now Eustrophus spake these things to us, not in jest, but because I did at that time studiously apply myself to the mathematics, and perhaps also in every thing to honor that saying, Nothing too much, as having been conversant in the Academy.