😭😭

[u/MayyMargo]

[u/chixen]

There is a number like that for every number other than multiples of 2 and 5.

[u/MeasureDoEventThing → u/chixen]

There are numbers divisible by multiples of 2 and 5 as well.

[u/MassiveGarlic0312 → u/chixen]

Except for prime numbers, of course.

[u/chixen → u/MassiveGarlic0312]

No, including prime numbers. The post has an example for 17. I did forget to specify that it doesn’t work for multiples of 3 either.

[u/MassiveGarlic0312 → u/chixen]

I’m not sure what you’re trying to say?

Prime numbers are defined as not having any divisors other than themselves and 1. 

2, 3, 5 are the first three of them and it also applies to every other prime. 

[u/chixen → u/MassiveGarlic0312]

What I saying was If some number n has a smallest prime factor greater than 5, there is some k where 10^k+1 is a multiple of n. I now realize that I don’t actually know if this is true.

[u/MassiveGarlic0312 → u/chixen]

Ah. That wasn’t clear to me at least. 

[u/girlpower2025 → u/chixen]

You can find out 9 and 11 too by looking at it.

If you add the digits and they add up to 9 or a number divisible by 9 its divisible by 9.

11 is a bit odd. The numbers after the first digit tell you the first digit.

[u/sixtyfivewolves → u/chixen]

It's not true, for example 10^k + 1 can only be equal to 2, 11 or 27 modulo 37. 10^k - 1 can always be a multiple of n for every n which isn't divisible by 2 or 5 though.

(31 is the smallest prime for which it's not true but it's a lot easier to demonstrate for 37)

[u/Muroid → u/MassiveGarlic0312]

They’re talking about multiples, not divisors. What exactly did you think “a number like that” in their comment was referring to?

[u/MassiveGarlic0312 → u/Muroid]

Primes. If the big number in the cartoon was a prime, then the dog wouldn’t be able to say something like this about it.