I just want to summarize what I learned in this thread in order to ensure that I understand it. As I understand, the steps for determining the rule should be something like this:

1. See sequence. 2. What relations do the elements share? All are numbers, integers, even, differ by two, and are in ascending order. The rule is likelier to contain each (but not all) of these as a clause than not to. 3. If any relation you thought of belongs to a larger class, add that class. 4. Try to disconfirm each relation by creating sequences that violate only this relation (as well as its descendents, necessarily). Test general attributes first, since if they fail, the descendents can be considered impossible. 5. Create a candidate rule which consists of all relations that were not disconfirmed. 6. Offer the rule to the examiner.

Quite a bit more laborious than blurting out "n[i] = n[i-1]+2", I have to admit.