Baltic Way 2020 · Problem 19
Number Theory
Denote by the number of positive divisors of a positive integer . Prove that there are infinitely many positive integers such that divides .
When you’re ready
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Review
Topics
Divisibility and factorization · Arithmetic functions
Solutions
Solution
Note that . Therefore all numbers with divisors that are divisible by satisfy the condition. There are infinitely many of those, for example, all numbers in the form , where is a prime different from .
Contest context
Results from Baltic Way 2020
10 teams
- Mean score
- 2.1 / 5
- Scores of 4 or 5
- 3 / 10
- Estonia
- 1 / 5
Score distribution
03
13
20
31
40
53
All team scores
| Team | Score |
|---|---|
| Germany | 5 / 5 |
| Norway | 5 / 5 |
| Poland | 1 / 5 |
| Finland | 5 / 5 |
| Latvia | 0 / 5 |
| Estonia | 1 / 5 |
| Denmark | 0 / 5 |
| Sweden | 1 / 5 |
| Lithuania | 3 / 5 |
| Iceland | 0 / 5 |