Cracking RSA with small plaintext
We have given $c = m^{17} \bmod (N=pqrk)$ with $k = p+q+r$
We can write this as $$m^{17} =  c + \ell (pqr)k$$ for some integer $\ell$.
Now consider this as $$m^{17} =  c + (\ell pqr)k$$
if $m &lt; k$ you can find the $m$ if not information is lost and the answer is not unique.