Friday the 13th is considered an unlucky day in Western superstition. It occurs when the 13th day of the month in the Gregorian calendar falls on a Friday, which happens at least once every year but can occur up to three times in the same year. In 2017, it occurred twice, on January 13 and October 13. In 2018, it also occurs twice on April 13 and July 13. There will be two Friday the 13ths every year until 2020, where 2021 and 2022 will have just one occurrence, in August and May respectively. – wikipedia
Thirteen is a reviled number since Babalyonian times. It has also been associated with the Last Supper; Jesus, the apostles and the one reviled, Judas the traitor.
Since 13 can only be divided evenly by 1 and 13 (itself), it is called a prime number. A prime number can only be divided evenly by one and itself. The other numbers such as 6, 12, and 21 are called composite numbers since they can have many factors (more than two).
List of prime numbers up to 100: 2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,
Do those seems like attractive numbers to you?
The preferences for all numbers up to 13 probably goes much deeper. Cognitive studies show that primates, crows and other higher functioning creatures that live in social groups have a preference for groups in numbers that can easily be divided.
The idea that certain calendar dates are lucky or unlucky is of ancient origin, going back as far as the Mesopotamian civilizations. Tables that identify lucky and unlucky days are sometimes known by the German label of Tagwählerei. The Coligny calendar also identifies certain calendar dates as lucky or unlucky, and the Roman fasti marks many days and parts of others as dies nefasti, unsuited for the conduct of public business. Contemporary North America preserves a tradition that Friday the 13th is an unlucky day. It has been called a “pervasive form of divination” that “is found in all societies which regulate their days and nights in calendric systems.”
The received idea concerning the origin of Tycho Brahe days was that “Tycho Brahe, the celebrated Danish astronomer of the sixteenth and seventeenth centuries, was very superstitious, considering certain days in the year pregnant with misfortune, wherefore in Denmark, up to this very day, the laboring class call such days on which they happen to meet with some unfortunate accident, Tycho Brahe’s days.” In his travelogue A Poet’s Bazaar, Hans Christian Andersen alludes to the fact that Tycho Brahe died in exile in Prague, observing that “Denmark owns not even his dust; but the Danes mention his name in their bad times, as if a denunciation proceeded out of it: ‘These are Tycho Brahe’s days!’ say they.”
However, no mention of the Tycho Brahe days is actually found in the work of Tycho Brahe. They nevertheless are often referenced in almanacs and recur in Scandinavian folklore. In the Cyprianus tradition, Tycho Brahe days are considered unlucky for magical work; several of the spells in the Black Books of Elverum note that they should not be carried out on a Tycho Brahe day.