It’s common knowledge that if the 13th of a month is a Friday you should be very careful or even better put off all your affairs and keep your head down. Just in case. You should be especially careful to do so if the Friday of the 13th occurs in the leap year. The horror of the horror is when Friday of the 13th happens in February of the leap year.
From the beginning of A.D. such Horror of the Horror days (Friday of the 13th in February of the leap year) there were as many as …
When calculating use the Gregorian Style. The last Friday the 13th was on 13 July, 2012.