Pick the odd number out: 3, 5, 9, 11, 14, 17, 21.

Introduction / Context:
One simple way to spot an odd one out is to look for parity differences (even vs odd), especially in a set dominated by odd numbers. The given list predominantly contains odd integers, with a single even intruder.

Given Data / Assumptions:

• Odd numbers present: 3, 5, 9, 11, 17, 21
• Even number present: 14

Concept / Approach:
The parity rule is decisive: only one term is even while all others are odd. Therefore that term is the odd one out in the broader sense of pattern matching.

Step-by-Step Solution:
Check parity: 3(O), 5(O), 9(O), 11(O), 14(E), 17(O), 21(O)Only 14 is even ⇒ odd-man-out

Verification / Alternative check:
Other properties (primality, divisibility) produce more than one mismatch. Parity uniquely isolates 14 here.

Why Other Options Are Wrong:
21/17/9 are odd numbers and conform to the majority pattern.

Common Pitfalls:
Overcomplicating with prime checks (e.g., 9 and 21 are composite); parity offers the cleanest single exception.

Final Answer:
14