Interesting hapenstance

My boss just sent out an e-mail informing us that our Bangalore office is closed today. Included in the e-mail was a quote from the site manager:

...just to let you know, that Friday Mar 21 is a holiday in BLR on account of Good Friday/Id-Milad/Holi religious celebrations !!

A very rare and special significance of this holiday particularly this year is that three major religions Christianity, Islam and Hinduism all have major religious significance on the same day (i don't ever recall any holiday where three religions had a festival on the same day) !!!

I wonder how often this happens -- especially since all three holidays drift according to the Gregorian calendar (or at least I presume they do since the Islamic calendar is strictly Lunar and drifts quite a bit, and the Hindu calendar is, like the Jewish calendar, more lunar and solar)