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:
- 109 different families of subsets of a three-element set whose union includes all three elements.
- 109 different loops (invertible but not necessarily associative binary operations with an identity) 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 (or Archimedean) tilings.
The decimal expansion of 1/109 can be computed using the alternating series, with <math>F(n)</math> the <math>n^{th}</math> Fibonacci number:
::<math>\frac{1}{109}=\sum_{n=1}^\infty{F(n)\times 10^{-(n+1)\times (-1)^{n+1}=0.00917431\dots</math>
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.
See also
- 109 (disambiguation)