According to Pythagorean number lore, odd numbers were thought to be male and even numbers were considered female. Some of the first few odd and even numbers were given human attributes. For example, the number two was associated with "opinion"; four was associated with "justice"; the number five was associated with "marriage" since it was the union of the first even number, 2, and what they considered to be the first odd number, 3. The number one was not considered to be a number at all, but was thought of as the divine generator of all numbers.
Source: Historial Topics for the Mathematics Classroom, 1989 (National Council of Teachers of Mathematics).