The Republic by Plato Part 8 Page 10

Now that which is of divine birth has a period which is contained in a perfect number (i.e. a cyclical number, such as 6, which is equal to the sum of its divisors 1, 2, 3, so that when the circle or time represented by 6 is completed, the lesser times or rotations represented by 1, 2, 3 are also completed.), but the period of human birth is comprehended in a number in which first increments by involution and evolution (or squared and cubed) obtaining three intervals and four terms of like and unlike, waxing and waning numbers, make all the terms commensurable and agreeable to one another. (Probably the numbers 3, 4, 5, 6 of which the three first = the sides of the Pythagorean triangle.

The terms will then be 3 cubed, 4 cubed, 5 cubed, which together = 6 cubed = 216.) The base of these (3)