Find the odd number out in the sequence: 1, 4, 9, 16, 20, 36, 49.

Problem restatement
From 1, 4, 9, 16, 20, 36, 49, choose the number that does not share the main property with the rest.

Given data

• Sequence: 1, 4, 9, 16, 20, 36, 49

Concept / Approach
The terms are largely perfect squares of small integers; check each.

Step-by-step validation
1 = 1² 4 = 2² 9 = 3² 16 = 4² 20 ≠ n² for integer n 36 = 6² 49 = 7²

All are perfect squares except 20.

Verification / Alternative
20 lies between 4²=16 and 5²=25, confirming it is not a perfect square.

Common pitfalls

• Assuming every term is a square by pattern recognition without checking 20 individually.

Final Answer
20