Friday the 13th one occurrence each. A Friday the 13th occurs during any month that begins on a Sunday. The fear of the number 13 has been given a scientific name: "triskaidekaphobia"; and on analogy to this the fear of Friday the 13th is called "paraskevidekatriaphobia", from the Greek words "Paraskeví" (Παρασκευή, meaning "Friday"), and "dekatreís" (δεκατρείς, meaning "thirteen"). The superstition surrounding this day may have arisen in the Middle Ages, "originating from the story of Jesus' last supper and crucifixion" in which there were 13 individuals present in the Upper Room on the 13th of Nisan Maundy Thursday, the night before his
Friday the 13th year being a common year starting on Tuesday (F) (e.g. 2001/02, 2012/13 and 2018/19), or from August to October the following year being a leap year starting on Saturday (BA) (e.g. 1999/2000 and 2027/28). The shortest period that occurs with a Friday the 13th is just one month, from February to March in a common year starting on Thursday (D) (e.g. 2009, 2015 and 2026). Each Gregorian 400-year cycle contains 146,097 days (with 97 leap days) or exactly 20,871 weeks. Therefore, each cycle contains the same pattern of days of the week and thus the same pattern of Fridays that