25 can be expressed as the sum of the first 5 consecutive odd numbers.
According to the provided reference, 25 can be expressed as the sum of the first 5 consecutive odd numbers: 1 + 3 + 5 + 7 + 9 = 25. This confirms that the blank should be filled with "5".
Therefore, 25 can be expressed as the sum of the first 5 consecutive odd numbers.
