In Pythagorean numerology, when dealing with base or root numbers from 1 to 9, there’s a strong emphasis on the distinction between odd and even numbers. Odd numbers are generally considered masculine, bright, courageous, and more favorable. Even numbers, on the other hand, are viewed as feminine, darker, more cautious, reserved, and generally less favorable.
While this perspective can to some extent be applied in Chaldean numerology as well, this system primarily classifies root numbers into what are referred to as strong and weak numbers. The strong numbers are 1, 3, 5, and 6. The weak numbers are 4 and 8. Numbers 2, 7, and 9 are considered more neutral.
The term “strong” here doesn’t refer to influence, physical strength, or self-confidence. For instance, nines are often physically robust and confident, and some sevens can be quite combative. In this context, “strong” refers more to a combination of ease and at least a certain degree of balanced energy—qualities that tend to bring positive outcomes.
In contrast, numbers 4 and 8 are generally seen as unbalanced, and thus often considered unfavorable. When operating in a negative way, these numbers can still be very powerful, but unfortunately not in a way that supports balance. For this reason, modern numerologists often refer to them as karmic numbers.
This classification into strong and weak numbers dates to ancient numerology. Some modern Chaldean numerologists put more emphasis on this division, while others give it less weight. Number 5 is sometimes regarded as more neutral, depending on the interpretation.
The Mystery of Numbers, Luck, Worlds and Planets 