Is there a set of integers where all differences are relatively prime?

50 Views Asked by At

Is there an infinite subset $\mathcal S\subset \mathbb Z$ with the property that for any 4-tuple of distinct elements $x,y,z,w\in \mathcal S$ $$ \gcd(x-y,z-w)=1? $$

1

There are 1 best solutions below

2
On BEST ANSWER

No. If $x,y,z,w$ are distinct and either all odd or all even, then the two differences are both even, and so $\gcd(x-y,z-w)\geq 2$. On the other hand, if $\mathcal{S}$ is infinite, then it contains either infinitely many even numbers or infinitely many odd numbers.