105 is an integer equal to 7!!.

Its prime factorization is 3 × 5 × 7.

It is part of a Ruth–Aaron pair with 104[1] using the formulation involving sums of prime factors.

It is the first Zeisel number.

The 105th cyclotomic polynomial is the first cyclotomic polynomial containing coefficients with absolute value larger than 1.

It is the smallest odd number, for which the cototient is larger than the totient.


  1. OEIS, Sequence A006145 (accessed 2021-02-09)
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