It happens that this occurs every 7-8 years.
I found a blog about this, but it does have a wee bit of foul language
or try googling “once every 823 years”
Did you know October 2010 has 5 Fridays, 5 Saturdays and 5 Sundays all in one month. The last time this happened was in 823! I haven’t personally checked this out, but so I heard. If someone wants to check and report back, let me know!