There are 12 hours on a clock, 12 months in a year ... at least). As the number immediately following this “perfect” one, 13 seemed flawed, inspiring unease throughout the ancient world.

Though 13 has a long but foggy history of ... superstition by people who believe they're seeing the number everywhere — glancing at a clock at precisely 11:11, for example.

Puzzlers were baffled as each opposite-facing number on the clock equalled '13' when added together. Users were asked to work out why the numbers equated to the exact same figure. In the ...