November 23 is Fibonacci Day, an annual holiday that honors one of the most influential mathematicians of the Middle Ages - Leonardo Bonacci.

November 23 is celebrated as Fibonacci day because when the date is written in the mm/dd format (11/23), the digits in the date form a Fibonacci sequence: 1,1,2,3.

The significance of these numbers extends beyond mathematics, as they often appear in nature, art, and architecture. Many natural patterns, such as the arrangement of leaves on a stem or the spiral of a seashell, follow the Fibonacci sequence.