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Not So Scary? 'Unlucky' 13's Other Meanings
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Feeling lucky? Today is Friday the 13th, one of only two of those most-unlucky days in 2017. (The other will come in October.)

The origins of Friday the 13th superstitions are a little murky, but folklore suggests that both Fridays and the number 13 gained notoriety separately. In Norse myth, for example, the disruptive god Loki was the 13th guest at a dinner party that turned deadly. Meanwhile, in Christian tradition, Friday is commemorated as the day when Jesus was crucified. [9 Common Superstitions, Explained]

But not everything about 13 is designed to induce triskaidekaphobia (fear of that number). Thirteen has other meanings as well. Here are a few.

In the Jewish tradition, boys come of age with a bar mitzvah ceremony at age 13. In some Jewish movements, girls also come of age with a bat mitzvah at 13. (In other movements, the age for girls is 12.)

"Bar mitzvah" means "son of the commandment," and "bat mitzvah" means "daughter of the commandment." At this age, Jewish children are considered morally responsible for themselves, and they take on new adult responsibilities. According to ReformJudaism.org, age 13 was likely chosen because it corresponded with the onset of puberty.

Not every culture considers 13 to be bad luck. In Italy, 13 is actually an auspicious number, "particularly when gambling," according to TuscanTraveler.com. Italy's version of the oft-feared 13 is the number 17. It has a nasty connotation because the way it's written in Roman numerals — XVII — can be rearranged to spell VIXI, Latin for "I have lived." (Note the past tense.) So, while 17 causes shudders in Italy, 13 gets a pass.

For adolescents, turning 13 means admission to PG-13 films. Turns out, PG-13 means violence. A paper published Jan. 11 in the journal Pediatrics found that box-office-topping PG-13 movies feature more gun violence than R-rated films.

Researchers first found in 2012 that PG-13 movies outpace R-rated movies in gun violence, and the new paper reveals that this trend is continuing. Gun violence in PG-13 films has doubled since 1985, the researchers in the new study reported.

"Our findings suggest that Hollywood continues to rely on gun violence as a prominent feature in its highly popular PG-13 action-oriented films," lead author Dan Romer, research director of the Annenberg Public Policy Center of the University of Pennsylvania, said in a statement. The difference between R-rated films and PG-13 films, the researchers wrote, is that the PG-13 movies leave out consequences like blood and suffering in the aftermath of violence.

The number 13 is an emirp. That's a number that's prime whether written forward or backward. Emirps don't include palindromic primes like 131; they're limited to numbers that are different forward and backward. Thirteen is the first of the emirps, followed by 17, 31, 37, 71, 73, 79 and 97.

In 1974, the Council of American Witches formally adopted a document of principles encompassing the basic precepts of Wiccanism, the belief system that draws on ancient Pagan customs and traditions. There were 13 of those precepts. The principles, according to ReligiousTolerance.org, include the practice of rituals to bring Wiccans closer to natural cycles, harmony with nature, belief in supernatural power, creative powers of the masculine and feminine, and a rejection of hierarchy.

Original article on Live Science.