See the link http://mathoverflow.net/q/165492/48849https://mathoverflow.net/q/165492/48849.
I think that my question (actually it is not originally my question, it is from someone on the AoPS) might suggest us to prove the Bertrand's Postulate in an elementary way (only if my question can be proved in an elementary way). But unfortunately I found that it has been downvoted and also labelled as "off-topic". Can anyone tell me the precise reason why it is considered as "off-topic"?