23

A Numerological Motif that serves as sort of the Evil Counterpart of The Hitchhiker's Guide to the Galaxy's 42. To put it simply, whenever you see the number 23, it hints towards a connection to the Ancient Conspiracy.

Originates in the Principia Discordia, but isn't an Arc Number there.

Examples of works that use 23 as an Arc Number:

Anime and Manga

This is the original name that Theophrastus Bombastus Von Hohenheim goes by in the Fullmetal Alchemist manga and Brotherhood adaptation.
It's also Hige's call-sign as a Manchurian Agent in Wolf's Rain.
In Magical Chronicle Lyrical Nanoha Force, the first arc is set mostly on Ruwella, a pastoral world where a Government Conspiracy conducted secret experiments on Lily Strosek (a driving force of the plot). According to TSAB's catalogue, Ruwella is the "Administrated World #23".

The Illuminatus Trilogy helped it get known.
It gets use as a Running Gag in Robert Rankin's "The Toyminator." (It's that kind of book.)

They Might Be Giants had a show in 1983 in which 23 was prevalent. The show was on January 23, John Linnell was 23 years old at the time, 23 people attended the show, they played 23 songs (although they had only planned to play 22), and Flansburgh and Linnell both earned $23.

The Roaring Twenties slang "23 Skidoo!", which means go away, scram, or GTFO.
Together with 28, one of the Arc Numbers in Wilhelm Fliess's Biorhythm theory.
Discordianism pretty much set the ball rolling on this one.
Allegedly, Gaius Julius Caesar was stabbed 23 times during his assassination.
- Seeing as about 60 senators set on him, this is barely more than a 1/3rd success rate. A number of them in fact wounded their allies. Also, according to Suetonius, only one of his wounds was fatal.
  - About 60 senators were part of the conspiracy, but there were only seven or eight assassins so it's closer to 3 per person.
The motor company Nissan whenever they launch a new race car in any series, will use the number 23 because Nissan sounds a bit like Ni-San or 2-3.