Theodorus of Cyrene was born in Cyrene and spent most of his
life in Athens, Greece. He was a Greek mathematician of the 5th
century BC who was admired by Plato (who mentions him in several of
his works). Little is known about him; however, Plato attributes to
him the first proof of the irrationality of the square roots of 3,
5, 6, 7, 8, 10, 11, 12, 13, 14, 15 and 17. The method he used is
not stated, but since he stopped at 17, it seems possible that he
used the traditional Pythagorean method of odds and evens, since 17
is the first number for which this method breaks down.