| Number: | 105 |
| Divisor: | 1, 3, 5, 7, 15, 21, 35, 105 |
105 (one hundred [and] five) is the natural number following 104 and preceding 106.
105 is a triangular number, a dodecagonal number,[1] and the first Zeisel number.[2] It is the first odd sphenic number and is the product of three consecutive prime numbers. 105 is the double factorial of 7.[3] 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 numbers less than a thousand are 9, 15, 195, and 825.
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. 105 is the product of the first three odd primes (
3 x 5 x 7
n=105
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-2k
0<k<log2(n)
k=8
105 is the smallest integer such that the factorization of
xn-1
\pm1
\pm1
105 is the number of parallelogram polyominoes with 7 cells.
105 is also: