[51] And in addition to this there is this point also of which we should not be ignorant, the number four is the first number which is a square, being equal on all sides, the measure of justice and equality. And that it is the only number the nature of which is such that it is produced by the same numbers whether in combination, or in power. In combination when two and two are added together; and again in power when we speak of twice two;[4] and in this it displays an exceedingly beautiful kind of harmony, which is not the lot of any other number.
If we examine the number six which is composed of two threes, if these two numbers are multiplied it is not the number six that is produced, but a different one, the number nine.