Distribution Each 400 year Gregorian solar cycle contains 146,097 days (with 97 leap days) or exactly 20,871 weeks. Each cycle contains the same pattern of days of the week and therefore the same pattern of Fridays that are on the 13th. The 13th day of the month is very slightly more likely to be a Friday than any other day of the week.
distribution each 400 year gregorian solar cycle contains 146097 days (with 97 leap days) or exactly 20871 weeks each cycle contains the same pattern of days of the week and therefore the same pattern of fridays that are on the 13th the 13th day of the month is very slightly more likely to be a friday than any other day of the week