Friday the 13th

[snopes]

Comment: On the topic of Friday the 13th:

It is interesting to note that, in the Gregorian calendar, the 13th is
more likely to be a Friday than any other day of the week.

I know, it sounds ridiculous. But wait!

In a 400 year cycle, there are 400*365 days, plus a number of leap days -
97, specifically. (100, -4 for centuries, +1 for 4-centuries.) That's
146,097 days, and that's divisible by 7, so every 400 year cycle gets the
same pattern of days, and by coincidence, the 13th is marginally more
likely to be a Friday than any other day.

[Stoneage Dinosaur]

True, according to scienceworld. Over a 400 year period there are apparently 688 Friday the 13ths, but only 684 Thursday or Saturday the 13ths.