this post was submitted on 03 Sep 2025
454 points (99.3% liked)

xkcd

14494 readers
150 users here now

A community for a webcomic of romance, sarcasm, math, and language.

founded 2 years ago
MODERATORS
 

xkcd #3137: Cursed Number

Title text:

Another group of mathematicians is working to put an upper bound on the number, although everyone keeps begging them to stop.

Transcript:

Transcript will show once it’s been added to explainxkcd.com

Source: https://xkcd.com/3137/

explainxkcd for #3137

top 27 comments
sorted by: hot top controversial new old
[–] badcommandorfilename@lemmy.world 40 points 4 months ago

print(uuid())

[–] palordrolap@fedia.io 31 points 4 months ago (2 children)

Felt like noodling a little with some numbers. I have a nice candidate. 22301. Pretty small, right? ~~It's prime.~~ That's not troubling to most anyone's sanity. Edit: one should check one's silly code more carefully before madly pretending to be mad on the Internet. It is not prime. But the intermediate numbers still are.

There's something that can be done to that number four times (but no more) which results in a prime each time and the fourth step results in a 70 digit number that I may have looked at slightly tOo LoNnNg.

Edit 2: Attempt at redemption for the math if not the joke: Start with 5497949 which is prime, and you can do the thing four times and get a prime each time. The last one has 108 digits and, no word of a lie, starts 6969...

Imaginary bonus points for guessing what the heck the operation / something is.b

[–] Audalin@lemmy.world 23 points 4 months ago (1 children)

But 22301 isn't prime? It's 29*769.

[–] palordrolap@fedia.io 33 points 4 months ago (1 children)

Well, this is embarrassing. This is what I get for mathing after midnight.

[–] porl@lemmy.world 8 points 4 months ago (1 children)

The true number messed you up so much you can't recall it any more.

[–] scathliath@lemmy.dbzer0.com 2 points 4 months ago

Can confirm, it stole my lunch money when I tried to see it, then gaslit me and told me my fiancee did. Truly a cursed number.

[–] jaupsinluggies@feddit.uk 8 points 4 months ago (1 children)

If you divide it by itself and add one, you can do that infinitely many times and get a prime every time. Works for all the primes.

[–] sga@piefed.social 1 points 4 months ago* (last edited 4 months ago)

it also works for all perfect numbers (by definition non prime), and also triangle numbers (all triangle numbers greater than 3 or non prime), and also for all numbers above 42, and below 69. quite a neat property sir.

[–] four@lemmy.zip 27 points 4 months ago (1 children)

A moment of silence for all those who sacrificed themselves in the name of science

[–] ZoteTheMighty@lemmy.zip 10 points 4 months ago

Actually, this isn't useful, so we still let it be called "math".

[–] IndustryStandard@lemmy.world 14 points 4 months ago (2 children)

The cursed number is pi. Everyone who tries to fully read it dies. This is why we shortened it to 3.14.

[–] UnrepententProcrastinator@lemmy.ca 5 points 4 months ago (2 children)
[–] whoisearth@lemmy.ca 4 points 4 months ago

Meh close enoigh

[–] Cocodapuf@lemmy.world 2 points 4 months ago

I like 22/7

[–] sga@piefed.social 4 points 4 months ago

everyone who has ever heard of pi, has either died, or will die. just thought of pi gives you a chronic illness which can not be cured

[–] DarkCloud@lemmy.world 9 points 4 months ago

Sounds like those stupid Rationalist cult groups who spend their time coming up with AI fantasies, and claim some thought-experiments are so powerful they'll ruin your mind - real immature stuff. Deserves to be lampooned like this.

[–] nialv7@lemmy.world 6 points 4 months ago (1 children)

If a number is long enough human won't be able to perceive it all at once, so in fact there are only finite number of cases we need to check.

[–] Jankatarch@lemmy.world 3 points 4 months ago

Human will run out of memory when reading the number, in fact.

[–] ripcord@lemmy.world 6 points 4 months ago (1 children)

Sounds like the seed of an SCP.

[–] Swedneck@discuss.tchncs.de 1 points 4 months ago

peep the horror

[–] Dasus@lemmy.world 4 points 4 months ago

Sure there's quite a lot of them to choose from, but for instance USPS tracking numbers are 22-digit numbers.

[–] tisktisk@piefed.social 4 points 4 months ago (3 children)

I'm confused, what is this new lower bound specifically?

[–] finalarbiter@lemmy.dbzer0.com 6 points 4 months ago

The number that makes people go insane is bigger than 2.6*10^21^, or 2,600,000,000,000,000,000,000

[–] pressanykeynow@lemmy.world 4 points 4 months ago

Works as intended then.

[–] ksigley@lemmy.world 3 points 4 months ago

There really is an xkcd for everything.

[–] ShinkanTrain@lemmy.ml 2 points 4 months ago

This is why they invented notation. Just to be safe