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105 (one hundred [and] five) is the natural number following 104 and preceding 106.

## In mathematics

105 is a triangular number, a 12-gonal number and a Zeisel number. It is a sphenic number, and is the product of three consecutive prime numbers. 105 is the double factorial of 7. It is also the sum of the first five square pyramidal numbers.

105 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. The distinct prime factors of 105 add up to 15, and so do those of 104, hence the two numbers form a Ruth-Aaron pair under the first definition.

105 is also a number n for which n - 2^k is prime, for 0 k log_2(n). (This even works up to k = 8, ignoring the negative sign.)

105 is the smallest integer such that the factorization of x^n-1 over Q includes coefficients other than \pm 1.

## In science

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 and ended on 1779 May. 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 and ended on 1882 October. The duration of Saros series 105 was 1316.2 years, and it contained 74 lunar eclipses.

105 is also:

## References

• Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group. (1987): 134

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