There’s no clear consensus regarding the folklore and superstition surrounding Friday, the 13th and the number 13 in general. Friday the 13th is said to be the unluckiest day of the year, but there are many people, including Taylor Swift, who would disagree.

Here are 13 facts and trivia on Friday, the 13th and the mysterious number 13.

1.Most hospitals, office buildings, and condominiums over 13 floors simply jump to the 14th floor, skipping the 13th. Also, many hospitals don’t have a room with the number 13 on it.

2. In mathematics, the number 13 is considered a “happy number.” Happy numbers are defined by a process of replacing a positive integer with the sum of the squares of its digits, repeating the process until the number equals one. Unhappy or sad numbers are any positive integer that cannot be reduced to one by this process and goes on forever.

**Happy Numbers 1-1,000:**

1, 7, 10, 13, 19, 23, 28, 31, 32, 44, 49, 68, 70, 79, 82, 86, 91, 94, 97, 100, 103, 109, 129, 130, 133, 139, 167, 176, 188, 190, 192, 193, 203, 208, 219, 226, 230, 236, 239, 262, 263, 280, 291, 293, 301, 302, 310, 313, 319, 320, 326, 329, 331, 338, 356, 362, 365, 367, 368, 376, 379, 383, 386, 391, 392, 397, 404, 409, 440, 446, 464, 469, 478, 487, 490, 496, 536, 556, 563, 565, 566, 608, 617, 622, 623, 632, 635, 637, 638, 644, 649, 653, 655, 656, 665, 671, 673, 680, 683, 694, 700, 709, 716, 736, 739, 748, 761, 763, 784, 790, 793, 802, 806, 818, 820, 833, 836, 847, 860, 863, 874, 881, 888, 899, 901, 904, 907, 910, 912, 913, 921, 923, 931, 932, 937, 940, 946, 964, 970, 973, 989, 998, 1000

3. Singer / Songwriter, Taylor Swift is said to draw the number 13 on her hand with eyeliner before every show, she apparently turned 13 years old on Friday, the 13th, and her song, “The Lucky One” is the 13th track on her album, Red. Oh, and there’s her Twitter handle: @taylorswift13.

4. Thirteen is the third centered squared number. In elementary number theory, a centered square number is a centered figurate number that gives the number of dots in a square with one dot in the center and all other dots surrounding that center point in successive square layers. The number 13 is also considered a center squared prime.

**Centered Squared Numbers 1-1,000:**

1, 5, 13, 25, 41, 61, 85, 113, 145, 181, 221, 265, 313, 365, 421, 481, 545, 613, 685, 761, 841, 925

5. Much of the superstition surrounding the number 13 dates back to ancient times. 13 follows the holy number 12, which represents “completeness” in Nature. There are 12 signs in the Zodiac, 12 months in a year, 12 hours on a clock, and the list goes on and on.

6. Nearly 20 million people are said to suffer from friggatriskaidekaphobia (also called paraskavedekatriaphobia), the fear of Friday, the 13th. The fear of the number 13 is called triskaidekaphobia, which we get from the Greeks (tris/three + kai/and + deka/ten + phobos/fear).

7. There are 13 Archimedean solids. In geometry, an Archimedean solid is a highly symmetric, semi-regular convex polyhedron composed of two or more types of regular polygons meeting in identical vertices.

8. The number 13 is the sixth prime number of an infinite list of primes. A prime number is a natural number (whole, non-negative number), greater than one, with no positive divisors other than itself and one.

**Prime Numbers 1-1,000:**

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, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997

9. One popular explanation for the fear of the number 13 states that various cultures around the world have used lunar-solar calendars for ages, with approximately 12.41 lunations per solar year. The 12 “true months” make up one year with a smaller, and often ominous, thirteenth month.

10. Thirteen is part of the Fibonacci sequence, which is a series of numbers where a number is found by adding up the two before it. The sequence can be found all throughout Nature and is used to make the Fibonacci Spiral, an approximation of the Golden Ratio.

11. In some ancient cultures, the number 13 represented femininity due to its correlation with the number of lunar (menstrual) cycles in one year. One theory suggests that as the solar calendar triumphed over the lunar, the number thirteen became an unlucky or cursed number.

12. The Ancient origins of a standard deck of playing cards are unclear, but many agree it came from Ancient Egypt with some even speculating the lost city of Atlantis. In it, there are 13 cards in each suit, from Ace to King, which are said to represent the 13 weeks in one season (hence the four suits). 13 x 4 = 52 cards (or weeks in one year).

13. President Franklin Roosevelt was said to suffer from a mild case of triskaidekaphobia. According to journalist and Roosevelt biographer, John Gunther, “Like most people with good luck, FDR was moderately—not excessively—superstitious. He hated Friday the thirteenth, he would never start an important trip on a Friday if he could help it, and he disliked sitting down with thirteen at dinner.” Strangely, FDR passed away on April 12th, 1945. It was a Thursday.

What do you think about Friday the 13th and the number 13 in general? Share your thoughts below.