Odd numbers are described as dynamic
The odd numbers are 1, 3, 5, 7, and 9. The source describes them as solar, active, and dynamic. They tend to add movement and initiative to a combination.
Even numbers are described as receptive
The even numbers are 2, 4, 6, and 8. The source describes them as lunar, magnetic, and more static. They can hold, receive, or stabilize energy rather than pushing it outward.
Friendly does not always mean productive
One of the more interesting points in the source is that friendly numbers may create ease but not always growth. Difficult combinations can make people alert and active. Compatibility is therefore more subtle than simply matching similar numbers.