Number Theory – Proving Existence of n Consecutive Positive Integers Not Powers of Primes

number theory

Prove for each positive integer $n$, there exists $n$ consecutive positive integers none of which is an integral power of a prime number.

I'm not getting a single idea of how to approach it. One I found was to show that $n$ consecutive integers should not be divisible by any prime but it didn't worked.

Thanks in advance.

Best Answer

Consider the system of $n$ congruences

$x\equiv 0\pmod{(2)(3)}$

$x\equiv -1\pmod{(5)(7)}$

$x\equiv -2 \pmod{(11)(13)}$

and so on, up to

$x\equiv -(n-1)\pmod{(p_{2n-3})(p_{2n-2})}$

where $p_i$ is the $i$-th prime.

By the Chinese Remainder Theorem, this system of congruences has infinitely many positive solutions $x$.

If $x$ is such a solution, then $x$ is divisible by $(2)(3)$, $x+1$ is divisible by $(5)(7)$, and so on.

It follows that none of $x$, $x+1$, and so on up to $x+(n-1)$ is a prime power.

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