109 (number)
109 is the natural number following 108 and preceding 110.109 is the 29th prime number, so it is a prime with a prime subscript. 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, and 109 squares on an infinite chessboard that can be reached by a knight within three moves.
