Let $n$ be a composite number so that it has at most one prime factor such that $p \leq \sqrt{n}$. Find all ways how you can factor $n$ and give examples.

My work:

We know that if $n$ is composite, there has to be at least one prime factor with such property. We also can deduce that for any other prime factors of $n$ - lets call them $q_i$ there can be at most one of them because $q_i^2 > n$. So the different ways you could factor $n$ I came up with are

1) $n=p^k$ - for example $16=2^4$. 2) $n=p^k \cdot q$ - for example $44 = 2^2 \cdot 11$. 3) $n=p\cdot q$ - for example $22 = 2 \cdot 11$.

Are there any ways that I am missing?

  • 2
    $\begingroup$ Looks good to me. Note that your case 3 ($n=p\cdot q$) is just case 2 with $k=1$. $\endgroup$
    – TonyK
    Mar 3, 2019 at 14:46

1 Answer 1


You already found out that at most one prime factor can exceed $\sqrt{n}$ (this is true for every positive integer $n$). Moreover, we know that we must have exactly one prime factor $p\le \sqrt{n}$ (Because of the mentioned condition).

If no prime factor exceeeds $\sqrt{n}$, then we must have a prime power.

If one prime factor exceeds $\sqrt{n}$, the exponent corresponding to this prime must be $1$, so we must have a prime power multiplied with this prime.

Hence , you did not overlook examples.


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