there are different myths why we have paraskevidekatriaphobia, or for the common language, the fear of Friday the 13th. One is because of the last supper of Jesus, where people sat at the table on the night from Thursday to Friday.
Another myth comes from the arrest of Jacques de Molay on a Friday the 13th. De Molay was the grand master of the knights templar. As this society was surrounded in so many myths, that people believe there is a course coming from them and has a connection with Friday the 13th.
I think the templars have been only another Christian knight order, same like many others. Yes, they had their special laws and rituals, but nothing different than others. They have been only very rich, as we can say they invented the modern money transfer.
If an organisation becomes to powerful, the one organisation on top spot will try to stop the one breathing in it's neck, and so did the pope, it destroyed the templars.
So, even if we have Tuesday the 13th, which is bad for Spanish and Greek culture, due to the connection with Mars, I don't believe in special unlucky and lucky days, this are only myths with a somehow historical background.