Let us write m=da and n=db. Here a and b are relatively prime integers and v=dab. Plugging this into the given equation we get da+3db−5=2dab−11d, so
da+3db−5=2dab−11d
which rearranges to
da+3db−2dab+11d=5
or
d(a+3b−2ab+11)=5
Since d is a positive integer, d must divide 5. Thus, d=1 or d=5.
First, let us assume that d=1. Then the equation can be rearranged into
a+3b−5=2ab−11
or
a+3b+6=2ab−11+6+5=2ab
so
a+3b+6=2ab
or
2ab−a−3b−6=0
or
a(2b−1)=3b+6
From here we conclude that 2b−1 divides 3b+6, so it must also divide 2(3b+6)−3(2b−1)=6b+12−6b+3=15.
Since 2b−1 is a positive integer there are four possibilities:
- If 2b−1=1, then b=1 and a=9.
- If 2b−1=3, then b=2 and a=4, which leads to a contradiction, since a and b should be relatively prime.
- If 2b−1=5, then b=3 and a=3, which is again a contradiction.
- If 2b−1=15, then b=8 and a=2, and once more this is not possible.
Hence, in this case we only have one solution, (9,1).
Now, assume that d=5. Then we can divide the equation by 5 and rearrange it to get
a+3b−1=2ab−11
or
a+3b+10=2ab
so
a(2b−1)=3b+10
This implies that 2b−1 divides 3b+10, so it must also divide 2(3b+10)−3(2b−1)=6b+20−6b+3=23.
There are two possibilities:
- If 2b−1=1, then b=1 and a=13.
- If 2b−1=23, then b=12 and a=2, a contradiction once more.
In this case we get the solution (65,5).
Therefore, the solutions are (m,n)=(9,1) and (65,5).