Here's the question you clicked on:
inkyvoyd
for any positive natural number n that has a prime factorization without the numbers {2,5}is it possible to multiply it by another number such that the result is a string of nines? note that the number of nines does not matter, what matters is that the result is just nines.
for 1 - 1*9=9 for 3: 3*3=9 for 7: 7*7=49 for 9: 9*1=9
for 11: 11*9=99 for 13: 13*?=????
The issue with this question is how to find such a given number
for 7: 7*142857=999999
Btw, I think I'll make this my problem of the day. It's simple math washed up a little so you don't recognize it.