Number series – find the incorrect term: 3, 7, 15, 27, 63, 127, 255

Introduction / Context:
This is a classic “Mersenne-like” sequence test where terms are one less than powers of 2. One value does not fit that model.

Given Data / Assumptions:

• Series: 3, 7, 15, 27, 63, 127, 255
• Exactly one term is wrong.
• Check against 2^n - 1 structure.

Concept / Approach:

Compute 2^n - 1 for n = 2, 3, 4, 5, 6, 7, 8 to see what the sequence should be.

Step-by-Step Solution:

Verification / Alternative check:

Replacing 27 with 31 restores the exact 2^n - 1 progression across all terms.

Why Other Options Are Wrong:

7, 15, 63, 127 match perfect Mersenne form with their respective exponents and are correct.

Common Pitfalls:

Looking for differences obscures the simpler power-of-two relationship.

Final Answer:

27