When mathematician John Forbes Nash suffered from schizophrenic delusions, he said that Life Magazine had run a cover story of him disguised as Pope John XXIII as his name was John and his favorite prime number was 23.
The smallest group of people where there is more than a 50% chance that 2 people will share the same birth day (day and month, not year).
A telegraphers' code meaning "line break".
Robert Anton Wilson's book, Cosmic Trigger I: Final Secret of the Illuminati, lists 23 as a cosmic number with strong connections to arcane magic and synchronicity. Numerous people have claimed to see 23's everywhere (the 23 curse) prior to enormous success and fruitfulness.
23 is the smallest odd prime that is not a twin prime
The 23 Enigma is a belief that the number 23 is of particular or unusual significance, especially in relation to disasters.