Thirteen

Thirteen for girls

The number 13 has long been the subject of superstition, supposedly arising from the discrepancy in months between the lunar and solar calendars. The solar calendar contains about 12.41 lunar cycles and the period between the last full moon of one year and the first of another is considered unlucky.

Thirteen for boys

Unlucky number thirteen is now an edgy baby name option thanks to Kourtney Kardashian and Travis Barker, who named their son Rocky Thirteen. They chose his one-of-a-kind middle name because "13 is just the greatest number of all time," according to Barker. Rocky is also the 13th Kardashian grandchild.

Many cultures around the world consider the number 13 to be bad luck. The dominant theory is that this arose because a calendar year contains slightly more than 12 lunar cycles, and that the time between the 12th and 13th full moons was particularly ominous.