A solution to last week's challenge can be found here. 
This Friday will be another Friday the 13th. Whether or not you consider yourself to be superstitious, odds are you're familiar with this dreaded calendar configuration.
But just how common are these occurrences? For this week's challenge, construct a workflow that provides a count of the number of Friday the 13ths for each year since 1900.
Bonus: Are there any years that don't have a Friday the 13th?
And for the bonus, I think we can prove that there will always be a Friday the 13th. We can ignore January and February due to leap year weirdness, and just prove that regardless of what day March the 13th will fall on, there will be a friday the 13th at some point in March-December. Here are the months:
Quick, fun challenge, meaning the associated video is also nice and short: https://www.youtube.com/watch?v=Tu587UuaMt0&list=PL18SpOXDj-KMUD4YwWC5vZaUsIa7drxNZ&index=45
