396, 462, 572, 427, 671, 264

In a digit-pattern “odd one out” series, each number is checked against a single digit-level rule, and the number where the rule fails is the exception. A common rule for 3-digit numbers is: the middle digit equals the sum of the outer (hundreds and units) digits.

1. 396: the outer digits 3 and 6 sum to 9, which equals the middle digit 9 -- the pattern holds.

2. 462: the outer digits 4 and 2 sum to 6, which equals the middle digit 6 -- the pattern holds.

3. 572: the outer digits 5 and 2 sum to 7, which equals the middle digit 7 -- the pattern holds.

4. 427: the outer digits 4 and 7 sum to 11, but the middle digit is 2 -- the pattern fails.

5. 671: the outer digits 6 and 1 sum to 7, which equals the middle digit 7 -- the pattern holds.

6. 264: the outer digits 2 and 4 sum to 6, which equals the middle digit 6 -- the pattern holds.

Since every number except 427 satisfies the rule that the middle digit equals the sum of the outer digits, 427 is confirmed as the number that breaks the pattern.

Hence, 427 is the number that does not follow the pattern.