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Odd one out: 3, 5, 7, 9, 11, 13

Published , last checked . Re-solved cold against the published wording before it went live: how puzzles and answers are checked.

One number does not belong with the primes in this short list. From the free puzzle set on Think Fanny. Next try When are clock hands at right angles?.

Think Fanny number puzzle formulas on a chalkboard

The puzzle

Which number is the odd one out?

3, 5, 7, 9, 11, 13

Look for the property shared by every number except one.

Verify the primes

Take none of this on trust. The primes are one of the best-documented sequences in mathematics, so the odd one out is checkable in under a minute:

If one of these contradicts the answer above, we would rather hear it than not. See how puzzles and answers are checked.