Philo Judaeus De Opificio Mundi 13

And he says that the world was made in six days, not because the Creator stood in need of a length of time (for it is natural that God should do everything at once, not merely by uttering a command, but by even thinking of it); but because the things created required arrangement; and number is akin to arrangement; and, of all numbers, six is, by the laws of nature, the most productive: for of all the numbers, from the unit upwards, it is the first perfect one, being made equal to its parts, and being made complete by them; the number three being half of it, and the number two a third of it, and the unit a sixth of it, and, so to say, it is formed so as to be both male and female, and is made up of the power of both natures; for in existing things the odd number is the male, and the even number is the female; accordingly, of odd numbers the first is the number three, and of even numbers the first is two, and the two numbers multiplied together make six.