You may ask me yes or no questions to come up with the rule on how I generated the following numbers: 2, 4, 6. The correct answer will receive my undying respect. Note: chess grand masters are most likely to figure this out.
This experiment was conceived by psychologist P. C. Wason and I read about it in The Black Swan, by Nassim Nicholas Taleb, not to be confused with the movie by the same name.
If you want more of a hint, e-mail me at firstname.lastname@example.org.