Thirteen is a prime number.

13 is a happy number as eventually reaches 1 when replaced by the sum of the square of each digit. For instance, 13 is a happy number because 1² + 3² = 10 and 1⁰ + 0² = 1.

Also:

• 13 is a Fibonacci number
• 13 is a lucky number
• A tridecagon has 13 sides.