109 (one hundred [and] nine) 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: There are 109 uniform edge-colorings to the 11 regular and semiregular (or Archimedean) tilings. The decimal expansion of 1/109 can be computed using the alternating series, with F(n) the n^{th} 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.

Other fields

109 is also the atomic number of meitnerium.