Citation from mathstackexchange answer to a question [duplicate]

In a paper in preparation, I want to refer to a formula that was given in MSE as an answer to a question. Because no reference was given to the source of that formula, and I couldn't obtain such a reference, I would like to ask:

1. Am I allowed to refer to the answer in my paper?
2. What should be mentioned in my citation?

Thanks for your answer!

• Remember that answers here are not peer-reviewed, so don't take a formula in an answer for granted if no source or explanation is given. For scientific papers you should not mention a formula without reference to a source that contains a proof. – TMM Sep 28 '13 at 13:00
• @TMM Thanks. I intent only to explain why the formula given is not allways applicable and that it is limited to assymptotical – Picard Porath Sep 28 '13 at 13:58