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Comment by jjtheblunt | Hacker News Reader

Fun math in action here: these two broods emerge every 13 and 17 years, respectively. Those two numbers are coprime, so their least common multiple, the next time a multiple of one will coincide with a multiple of the other, is 13 * 17 = 221, which subtracted from 2024 is 1803, when Thomas Jefferson was president and the previous time the broods emerged in the same year.

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When I schedule periodic tasks I always use prime numbers for the loop time. That way it's less likely that tasks will be run at the same time.

It's not really that important, but I do it as a form of tribute to the cicadas.

Of course, you still need the worst case when they overlap to meet performance requirements, and you just made testing that that much harder.

With enough tasks and/or small enough timing precision, that worst case may only occur once every thousand years or more.

Haruki Murakami, is that you?

Thats from the article

The simultaneous appearance of the two cicada broods – known as Brood XIX and Brood XII – is a rare event, not having occurred since 1803, a year when Thomas Jefferson was US president

Right but the article didn’t explain the calculation

Also to the point: the reason that the breeding cycles of these species are prime numbers of years is that it makes it less likely for a successful predator to evolve. To be a successful specialized predator of these species, your feeding cycle has to be a multiple of their breeding cycle which in practical terms means, since the cycles are so long, it has to be a exact match.

The 13s also get 17-1 breeding iterations without shared food competition from the 17s, etc, during the breeding days. The coprime periods effect strong attraction to the involved prime periods.

True but that’s less of a factor because the two species don’t have a lot of geographic overlap.

Here's a map to support your observation.

https://stateimpact.npr.org/pennsylvania/2019/05/20/everythi...

Crypto mating will eventually be a human endeavour

I want my broods named like my superbowls and final fantasy games.

Legend has it that these strange-looking numbers date to even older than the NFL and Squre Enix! :O

https://en.m.wikipedia.org/wiki/Roman_numerals

I'm really curious how the broods 'know' when to pop out.

Tiny clocks.

https://www.scientificamerican.com/article/how-do-periodical...

Some how they keep track of the growing cycle of the trees they feed on.

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