Prime numbers are intriguing numbers that are greater than 1 and can be evenly divided only by themselves and 1.

The four smallest prime numbers are 2, 3, 5 and 7. Next comes 11, which is quite a “jump” from 7.

What law is at work here? Mathematicians have been racking their brains since ancient times.

The numbers 13 and 17 are also prime numbers, and so-called “periodical” cicadas have life cycles of exactly 13 or 17 years.

This year, trillions of those creatures are emerging in various U.S. states, including Illinois.

This phenomenon is due to two different broods of cicadas emerging from underground simultaneously for the first time in 221 years.

Apparently, they don’t travel far from home. American videos show them clinging onto tree trunks, walls of residences—and just about anywhere—in enormous clusters.

The Japanese haiku poet Matsuo Basho (1644-1694) famously described the sound of cicadas as “iwa ni shimiiru” (literally, “seeping into the crags”).

But there is nothing sensitive or poetic whatsoever about the ear-splitting chorus of a battalion of cicadas, according to a researcher who developed a temporary hearing disorder after being surrounded by a mega-swarm.

In his book titled “Sosuzemi no Nazo” (Mystery of periodical cicadas), biologist Jin Yoshimura theorizes that their life cycles of 13 or 17 years evolved as a survival strategy.

The least common multiple is defined as the smallest multiple that two or more numbers have in common.

Prime numbers have large least common multiples.

Since 13-year or 17-year periodical cicadas always emerge at different times from other broods, they can breed and multiply among themselves without competition.

I feel like asking those bugs, “How on earth did you learn something so complex while you were underground?”

Summer weather prevailed yesterday in most parts of Japan. But I suppose it’s still too early for most Japanese cicadas to emerge, except for those in Okinawa. The wait is nothing, considering their fellows have remained underground patiently for 17 years.

When 1 is divided by 17, the answer, a recurring decimal, comes to 0.0588235294117647 ...

From the 17th digit after the decimal point, you start again with 058, ad infinitum. This is like the life cycle of cicadas. Prime numbers are intriguing numbers indeed.

—The Asahi Shimbun, June 6

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Vox Populi, Vox Dei is a popular daily column that takes up a wide range of topics, including culture, arts and social trends and developments. Written by veteran Asahi Shimbun writers, the column provides useful perspectives on and insights into contemporary Japan and its culture.