Given a positive integer , let be the product of the non-zero digits of . (If has only one digits, then is equal to that digit.) Let What is the largest prime factor of ?
Problem 1283
Official solution
1. Understanding the Problem:
We need to find the sum of the products of the non-zero digits of all numbers from 1 to 999. For a number , is defined as the product of its non-zero digits.
2. Breaking Down the Problem:
We can consider the numbers from 1 to 999 as three-digit numbers by padding with leading zeros if necessary. For example, 5 can be considered as 005.
3. **Calculating for Each Digit:**
- For a single-digit number , .
- For a two-digit number , if and .
- For a three-digit number , if .
4. **Summing for All Numbers from 1 to 999:
We need to consider the contribution of each digit position (hundreds, tens, and units) separately.
5. Contribution of Each Digit Position:**
- Each digit from 1 to 9 appears in each position (hundreds, tens, units) exactly 100 times in the range from 1 to 999.
- The sum of the non-zero digits from 1 to 9 is .
6. Calculating the Total Sum:
- For each digit position, the sum of the products of the non-zero digits is (since each digit from 1 to 9 appears 100 times).
- Therefore, the total sum for each position is .
7. Combining the Contributions:
- Since there are three positions (hundreds, tens, units), the total sum is .
8. Correcting the Calculation:
- We need to consider the product of the non-zero digits for each number. For example, for 105, .
- The correct approach is to consider the product of the sums of the non-zero digits for each position.
9. Revisiting the Calculation:
- The sum of the products of the non-zero digits for each position is .
- Therefore, the total sum is .
10. Final Calculation:
11. Finding the Largest Prime Factor:
- We need to find the prime factors of 97336.
- The prime factorization of 97336 is .
- The largest prime factor is 11567.
The final answer is .