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

Cardinal	one hundred [and] five
Ordinal	105th
Factorization
Divisors	3, 5, 7, 15, 21, 35
Roman numeral	CV
Binary	1101001
Hexadecimal	69

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 science

• The atomic number of hahnium, also known as dubnium.

In astronomy,

Messier object M105, a magnitude 11.0 elliptical galaxy in the constellation Leo

The New General Catalogue object NGC105 , a magnitude 13.2 spiral galaxy in the constellation Pisces

Asteroid 105 Artemis

The Saros number of the solar eclipse series which began on 499 March 27 and ended on 1779 May 16. The duration of Saros series 105 was 1280.1 years, and it contained 72 solar eclipses.

The Saros number of the lunar eclipse series which began on 566 August 16 and ended on 1882 October 26. The duration of Saros series 105 was 1316.2 years, and it contained 74 lunar eclipses.

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.