109 (number)

109 is the natural number following 108 and preceding 110.

In mathematics

109 is the 29th prime number. As 29 is itself prime, 109 is the tenth super-prime. The previous prime is 107, making them both twin primes.
109 is a centered triangular number.
There are exactly:

109 different families of subsets of a three-element set whose union includes all three elements.
109 different loops on six elements.
109 squares on an infinite chessboard that can be reached by a knight within three moves.

There are 109 uniform edge-colorings to the 11 regular and semiregular tilings.
The decimal expansion of 1/109 can be computed using the alternating series, with the Fibonacci number:
The decimal expansion of 1/109 has 108 digits, making 109 a full reptend prime in decimal. The last six digits of the 108-digit cycle are 853211, the first six Fibonacci numbers in descending order.