I believe there was an episode of Numb3rs in which two mathematicians were getting married, and were using the various formulas to find a day to get married that didn't coincide with any other celebrations. Eventually one of their parents "conceded" an anniversary. (I think.)
The point is, no matter how hard you try to avoid it, this may still happen.
_________________
When I allow it to be
There's no control over me
I have my fears
But they do not have me