Plutarch, De Iside et Osiride
Frank Cole Babbitt, Ed.

The Egyptians have a legend that the end of Osiris s life came on the seventeenth of the month, on which day it is quite evident to the eye that the period of the full moon is over.¹ Because of this the [p. 103] Pythagoreans call this day ‘the Barrier,’ and utterly abominate this number. For the number seventeen, coming in between the square sixteen and the oblong rectangle eighteen, which, as it happens, are the only plane figures that have their perimeters equal to their areas,² bars them off from each other and disjoins them, and breaks up the ratio of eight to eight and an eighth³ by its division into unequal intervals.

Some say that the years of Osiris's life, others that the years of his reign, were twenty-eight⁴; for that is the number of the moon's illuminations, and in that number of days does she complete her cycle. The wood which they cut on the occasions called the ‘burials of Osiris’ they fashion into a crescent-shaped coffer because of the fact that the moon, when it comes near the sun, becomes crescent-shaped and disappears from our sight. The dismemberment of Osiris into fourteen parts they refer allegorically to the days of the waning of that satellite from the time of the full moon to the new moon. And the day on which she becomes visible after escaping the solar rays and passing by the sun they style ‘Incomplete Good’; for Osiris is beneficent, and his name means many things, but, not least of all, an active and beneficent power, as they put it. The other name of the god, Omphis, Hermaeus says means ‘benefactor’ when interpreted.