109 (number)

109 (one hundred [and] nine) is the natural number following 108 and preceding 110.

In mathematics

109 is the 29th prime number, so it is a prime with a prime subscript.^[1] The previous prime is 107, making them both twin primes.^[2] 109 is a centered triangular number.^[3]

There are exactly 109 different families of subsets of a three-element set whose union includes all three elements,^[4] 109 different loops (invertible but not necessarily associative binary operations with an identity) on six elements.^[5] and 109 squares on an infinite chessboard that can be reached by a knight within three moves.^[6]

In other fields

109 is also the atomic number of meitnerium.^[7]

See also

• List of highways numbered 109

References