Odd One Out — Among the integers 6, 15, 12, and 17, identify the single prime and justify why the others are composite.

Introduction / Context:
A quick primality screen separates one candidate from several small composites.

Given Data / Assumptions:

• Numbers: 6, 15, 12, 17.
• Prime definition: exactly two positive divisors.

Concept / Approach:
Test divisibility by small primes (2, 3, 5).

Step-by-Step Solution:
6 = 2 * 3, composite.12 = 3 * 4 or 2 * 6, composite.15 = 3 * 5, composite.17: not divisible by 2, 3, or 5; therefore prime.

Verification / Alternative check:
Square root of 17 is about 4.12, so testing primes up to 3 suffices.

Why Other Options Are Wrong:

• 6: composite.
• 12: composite.
• 15: composite.

Common Pitfalls:
Assuming 15 is prime because it is not even; oddness does not imply primality.

Final Answer:
17