Numerology is the science of numbers. This is not to be confused with mathematics, but instead means to investigate the spiritual, magical or even psychological meaning of numbers. Numerology on Discworld differs greatly from numerology on Earth or Roundworld as it is sometimes called. On earth numbers such as three or seven have a special meaning in many cultures. This is not the case on Discworld where the most prominent number is eight.
Occurrance of the number eight:
- Eight is the number of magic.
- The eighth color of the rainbow is octarine and can only be seen by wizards (by virtue of the octagons in their eyes), witches (ditto) and other magical creatures. It is The Colour of Magic. In some rare instances, non-magical people can see it as an eye-watering blank space where a color should be.
- The Creator used eight spells to create the Discworld and these spells have been written down in the Octavo.
- The symbol of magic is the octogram, an eight-sided star.
- The eighth son of an eighth son always has magical abilities and has the right to study at Unseen University.
- The eighth son of an eighth son of an eighth son is a Sourcerer - a Source of Magic.
- 7a is the number of Bel-Shamharoth. His temple has two to the power of three sides.
- There are eight orders of wizardry at the Unseen University.
- There are eight days in a Discworld week. Hence a Watchman being on-duty 24/8.
- A Rat King made with eight rats, such as Spider, has greater psychic power, able to control not just other rats but people as well.
Because of the things associated with the number eight, no sane person on Discworld would ever write it down or pronounce it. Instead the usage of 7a is rather common. Certainly no wizard would ever say "eight". Rincewind's room at UU was 7a. He wasn't surpised.
Very potent numbers are also 8*8, 14.14, 57, and 88.
While fear of the number between seven and nine might be called "Octophobia," phobias are irrational fears, and, on the discworld, fear of 2³ is quite rational.