109 is the natural number following 108 and preceding 110.

One hundred nine (British English: One hundred and nine)is the 29th prime number. The previous prime is 107, making them both twin primes. 109 is a centered triangular number. 109 is the smallest number which is palindromic in bases 5 and 9.

One hundred nine is also:

• The atomic number of meitnerium.
• The registry number of the famous patrol boat PT-109, commanded by John F. Kennedy.
• The year AD 109 or 109 BC.