The given options are:
a) 525
b) 39
c) 24
d) 426
e) 636

To determine which number does not belong to the group, we need to identify a pattern or common characteristic among the other numbers.

Pattern Analysis:
- The numbers 525, 24, and 636 are all divisible by 3.
- The numbers 525, 39, and 426 are all multiples of 3.
- The numbers 24, 636, and 426 are all even numbers.

From the analysis, we can see that the number 39 does not have any common characteristics with the other numbers. Therefore, the number 39 does not belong to the group.

Explanation:
- The numbers 525, 24, and 636 are all divisible by 3. Divisibility by 3 can be determined by adding up the digits of a number and checking if the sum is divisible by 3. For example, 525: 5 + 2 + 5 = 12, which is divisible by 3.
- The numbers 525, 39, and 426 are all multiples of 3. This means they can be evenly divided by 3 without leaving a remainder.
- The numbers 24, 636, and 426 are all even numbers, meaning they are divisible by 2 and do not have a remainder when divided by 2.

However, the number 39 does not fit any of these patterns. It is not divisible by 3, it is not a multiple of 3, and it is not an even number. Therefore, the number 39 does not belong to the group.