Another Sesame Street Moment

[vakkotaur]

One of these things is not like the other.
One of these things does not belong.

Corrected version...
One of these things is not like the others,
One of these things just doesn't belong,
Can you tell which thing is not like the others...

                    _______
                   |   |   |
                   | 1 | 2 |
                   |___|___|
                   |   |   |
                   | 3 | 4 |
                   |___|___|

Maybe this isn't the best combination as I can see at least two answers to this.

Comments

[altivo.livejournal.com]

1, 2, and 3 are prime numbers, but 4 is not.

(By my definition, an integer that is evenly divisible only by 1 and itself is prime. Thus 1 qualifies.)

1, 2, and 4 form a sequence in which each successive term is twice the previous term. The next number in the sequence would be 8. 3 does not belong in that.