In planetary magic, there is an association between the seven planets as known by the ancients and the numbers 3 to 9. The so called planets include what we know today to be a star, the sun, and a satellite, the moon.
It is easy to remember those seven ‘planets’ as they are associated to the days of the week. The association may not be obvious in English but is easier to spot in other European languages.
The attribution of the planetary numbers is based on an order that can be obtained from the sequence of the days of the week. To find this order, starting from Moon (Monday), just take the planets every other day. Moon as the highest number, 9, and Saturn the lowest, 3.
We can find the same ordering on the back of the chair of Durer’s Astrologer, the character for moon being hidden by the pillow on which the astrologer is sitting.