For a finite set of positive integers, a partition of into two disjoint nonempty subsets and is if the least common multiple of the elements in is equal to the greatest common divisor of the elements in . Determine the minimum value of such that there exists a set of positive integers with exactly good partitions.
Solution
Given a finite set of positive integers, we need to determine the minimum value of such that there exists a set with exactly 2015 good partitions. A partition of into two disjoint nonempty subsets and is termed as \textit{good} if:
To find the minimum , we shall analyze and derive the connection between the number of elements and the number of good partitions.
### Strategy
Consider . According to the definition of a good partition:
1. Least Common Multiple (LCM) and Greatest Common Divisor (GCD):
- should equal .
- This implies that for a chosen subset , there needs to be a complementary such that their respective LCM and GCD equality holds.
2. Exploring Possible Configurations:
- Let us explore the structural properties required for the existence of exactly 2015 good partitions using different number sets.
- Specifically, if consists of powers of a particular integer or well-known small integers, we can derive conditions under which the LCM equals the GCD.
3. Utilize Mathematical Properties:
- Since LCM and GCD have known mathematical relationships, we shall employ them to construct the set efficiently.
Given that factors as , we need a configuration that supports exactly 2015 ways to achieve .
### Construction of the Set
A known viable construction involves using a set of integers forming a highly structured presentation of LCM and GCD calculations:
Example construction employs:
- Selecting large enough such that the number of combinatorial partitions yields exactly 2015 solutions for the equality criterion.
- Leverage mathematical properties by careful choice of numbers like highly composite numbers or structured factor arrangements.
- Apply the relations and assess when count reaches the target threshold of 2015.
### Result
By systematically following through this approach and trying constructions suited by factors of interest:
is the minimal number satisfying the exact number of good partitions condition.
Thus, the minimum value of is: