Find all integers such that is a product of two or more consecutive integers.
Solutions — 2
Solution 1
We will prove that is never a multiple of 3. This is clear if is a multiple of 3. If
is not a multiple of 3, then , where is the only term not divisible by 3. Thus is never the product of three or more integers.
It remains to discuss the case when for some integer . We write this as or . A check shows that among and only satisfies the requirement, as . Now let . The identities and indicate that for . But is odd, so it can equal or . We investigate them one by one.
If , which is impossible, as 5 is not a perfect square.
If which also fails.
Also fails.
If which also fails.
Finally, if , then , whence that we already found. Thus the only solution is .
Solution 2
To solve the problem of finding all integers such that is a product of two or more consecutive integers, we can follow these steps:
1. Check for the product of three or more consecutive integers:
- If is a product of three or more consecutive integers, it must be divisible by 3.
- We check the expression modulo 3:
- For :
- For :
- For :
- Since or , it is never divisible by 3. Therefore, cannot be a product of three or more consecutive integers.
2. Check for the product of two consecutive integers:
- Let .
- This implies:
- Completing the square on the left-hand side:
- Let , then:
- We need to be a perfect square. Let's check the range for :
- For , the inequality holds, so we only need to check values for .
3. **Check values for :**
- For :
- For :
- For :
- For :
- For :
- For :
- For :
- For :
- For :
- For :
Conclusion:
The only integer such that is a product of two or more consecutive integers is .
The final answer is .