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Prime numbers so memorable that people hunt for them

scientificamerican.com

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Re: Prime numbers so memorable that people hunt for them

#71

Post by dhosek »

tkgally wrote: post #62

My family’s phone number when I was a child was both a palindrome and a prime: 7984897. My parents had had the number for two decades without noticing it was a palindrome. I still remember my father’s delight when he got off a phone call with a friend: “Doug just said, ‘Hey, I dialed your number backwards and it was still you who answered.’ I never noticed that before!” A few years later, around 1973, one of the othe…

I thought everybody factors phone numbers. I also factor the odometer reading in my car while driving.

Re: Prime numbers so memorable that people hunt for them

#72

Post by nlh »

stevelosh wrote: post #36

If you were around in the 80's and 90's you might have already memorized the prime 8675309 ( https://en.wikipedia.org/wiki/867-5309/Jenny ). It's also a twin prime, so you can add 2 to get another prime (8675311).

My other favorite fun fact about this number (other than this new prime info which I am excited to have learned) is that in almost every store I’ve tried it, someone has used that (along with a local area code) as the phone number for a store loyalty card.

I’m a Bay Area guy, so if you’re ever at Safeway and need to get the discount without giving up your personal info, 415-867-5309 has got ya covered ;)

Re: Prime numbers so memorable that people hunt for them

#74

Post by freedomben »

out-of-ideas wrote: post #69
jedberg wrote: post #65

Earlier quoted context omitted.

I was around in the 80s, but this is awesome new information!

lol i didnt realize this was a prime number but i re-use this number any time i need a fake phone number in some sample/example data (im pretty certain nobody gets the reference, or takes the time to read it)

I do the same thing! Downside is every time I read my tests I get that song stuck in my head. Upside is it's a joy for some people when they discover it in the test

Re: Prime numbers so memorable that people hunt for them

#76

Post by oneshtein »

xigency wrote: post #17

Doesn't take very much searching to find this pretty nifty palindrome prime: 3,212,123 (the 333rd palindrome prime) Interestingly, there are no four digit palindrome primes because they would be divisible by 11. This is obvious in retrospect but I found this fact by giving NotebookLM a big list of palindrome primes (just to see what it could possibly say about it over a podcast). For the curious, here's a small set o…

11111111111111111111111 is prime (1©23)

Re: Prime numbers so memorable that people hunt for them

#77

Post by fancy_pantser »

nlh wrote: post #72
stevelosh wrote: post #36

If you were around in the 80's and 90's you might have already memorized the prime 8675309 ( https://en.wikipedia.org/wiki/867-5309/Jenny ). It's also a twin prime, so you can add 2 to get another prime (8675311).

My other favorite fun fact about this number (other than this new prime info which I am excited to have learned) is that in almost every store I’ve tried it, someone has used that (along with a local area code) as the phone number for a store loyalty card. I’m a Bay Area guy, so if you’re ever at Safeway and need to get the discount without giving up your personal info, 415-867-5309 has got ya covered ;)

You can use the number with your local area code just about anywhere at the pump to get a gas discount as well (a common loyalty reward program benefit).

Re: Prime numbers so memorable that people hunt for them

#78

Post by isaacfrond »

Since prime numbers are very useful in secure communication, such easy-to-remember large prime numbers can be of great advantage in cryptography,

That's nonsense. I'm sure there thinking of RSA, but that needs secret prime numbers. So easy-to-remember is pretty much the opposite of one want. Also they are way to big. 2048 bit RSA needs two 300 digit prime numbers.

Re: Prime numbers so memorable that people hunt for them

#79

Post by lambertsimnel »

norswap wrote: post #61
lambertsimnel wrote: post #34

...in decimal. https://t5k.org/notes/words.html points out that "When we work in base 36 all the letters are used - hence all words are numbers." Primes can be especially memorable in base 36. "Did," "nun," and "pop" are base-36 primes, as is "primetest" and many others.

Why use base 36 and not base 26?

We certainly could, but we already use 0-9 and then letters for hexadecimal. Using all 26 letters for base 36, but not base 26, is just an extension of that.

Re: Prime numbers so memorable that people hunt for them

#80

Post by ramchip »

hatthew wrote: post #57

> Since prime numbers are very useful in secure communication, such easy-to-remember large prime numbers can be of great advantage in cryptography What's the use of notable prime numbers in cryptography? My understanding is that a lot of cryptography relies on secret prime numbers, so choosing a notable/memorable prime number is like choosing 1234 as your PIN. Are there places that need a prime that's arbitrary, larg…

A lot of public-key cryptography is based on finite fields, and the integers modulo N combined with addition and multiplication form a finite field iff N is prime. This brings some extremely useful properties e.g. every non-zero element has a multiplicative inverse. N must also be public so people can compute things (e.g. to verify a signature), and big to resist brute force attacks.
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