Arrange the positive even numbers into groups according to the following rule: , , , , , we call "" the first number in the second group, "" the second number in the fourth group. If "" is the -th number in the -th group, then .
Problem 188
Official solution
To solve the problem, let's break down the solution step by step, closely following the original solution provided:
1. Identify the Position of 2024 in the Sequence of Even Numbers:
- Each positive even number can be expressed as for some positive integer .
- Since , it means is the -th even number in the sequence of all even numbers.
2. **Determine the Group Number () for 2024:**
- The sum of the first positive integers is given by the formula .
- The groups are formed by consecutive even numbers, with the st group having number, the nd group having numbers, and so on.
- We need to find the group () such that the total count of numbers up to that group is just before or equal to .
- For , the total count is .
- For , the total count is .
- Therefore, falls into the -th group because .
3. **Determine the Position () of 2024 Within Its Group:**
- To find , we calculate how far is from the start of its group.
- The difference between and the total count up to the previous group (-th) is .
- This means is the -nd number in the -th group.
4. **Calculate :**
- With (position in the group) and (group number), we find .
Therefore, the final answer, following the rules and format specified, is .