105 (one hundred [and] five) is the natural number following 104 and preceding 106. It is the double factorial of 7.

In mathematics

105 is a triangular number and a 12-gonal number as well as a sphenic number and a Zeisel number. It comes in the middle of the prime quadruplet (101, 103, 107, 109). The only other such odd numbers less than a thousand are 15, 195 and 825. 105 is also a pseudoprime to the prime bases: 13, 29, 41, 43, 71, 83 and 97.

One hundred five is also a number n for which n - 2^k is prime, for k < log₂(n). (This even works up to k = 8, ignoring the negative sign.)

In other fields

105 is also:

• The atomic number of hahnium, also known as dubnium.
• The designation of some spur routes of Interstate 5.
• A film format introduced by Kodak for their first folding camera. See 120 film.
• The number of surat al-Fil in the Qur'an.
• The year AD 105 or 105 BC.