105 (one hundred [and] five) is the natural number following 104 and preceding 106.
[4] 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).
105 is also the middle of the only prime sextuplet (97, 101, 103, 107, 109, 113) between the ones occurring at 7-23 and at 16057–16073.
In contrast, n ± 6, ± 10, ± 12, and ± 14 must be composite, making a prime gap on either side.
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.
, ignoring the negative sign.)
105 is the smallest integer such that the factorization of
In other words, the 105th cyclotomic polynomial, Φ105, is the first with coefficients other than
105 is the number of parallelogram polyominoes with 7 cells.