23

23 is the ninth prime number, the smallest odd prime that is not a twin prime.

23 is one of only two integers that needs nine (positive) cubes to represent it: 23 = 2³ + 2³ + 1³ + 1³ + 1³ + 1³ + 1³ + 1³ + 1³.

There were 23 problems on David Hilbert’s list of unsolved mathematical problems, presented to the International Congress of Mathematicians in Paris in 1900.

For 23 or more people in a room, the probability that two people have the same birthday is greater than 50%.

23! is 23 digits long.

The speed limit on campus at Tulane University.

Sources: Number Gossip; Wikipedia
Photo: M. Pearson