(p,q,r)∈{(3,2,7),(5,3,5),(7,3,2)}
We can rewrite in the form
q(r+1)pr+p−4q=1⇒pr+p−4q=qr+q⇒r(p−q)=5q−p.
Hence p=q
r=p−q5q−p=p−q4q+q−pi.e.r=p−q4q−1.
So p−q=q, p−q=2q, p−q=4q. We have p−q=1 or p−q=2 or p−q=4.
i) If p−q=1 then q=2,p=3,r=7.
ii) If p−q=2 then p=q+2,r=2q−1.
If q≡1(mod3) then q+2≡0(mod3), q+2=3⇒q=1 contradiction.
If q≡−1(mod3) then r≡−2−1≡0(mod3), so r=3,q=2,p=4 contradiction.
Hence q=3,p=5,r=5.
iii) If p−q=4 then p=q+4,r=q−1. Hence q=3,p=7,r=2.