Problem:
Determine all pairs of a positive integer and a prime number satisfying the equation
, 2022
Solutions — 2
Solution 1
Solution:
Rewriting the equation as , we see that must divide . However, since is prime, the only positive factors of are , and . We now check each case separately:
Case :
The equation becomes . Since this would imply that divides , we do not get any solutions in this case.
Case :
The equation becomes and cancelling a factor of we find that . The pair is therefore the only solution in this case.
Case :
The equation becomes and after cancelling, we get . Again, this would imply that divides , which is not possible. No solutions in this case.
We conclude that is the only pair satisfying the equation.
Solution 2
Solution:
We observe that divides the left-hand-side of the equation and therefore must divide the right-hand-side as well. Now if divides , we must have that divides . Let us write for some positive integer . Substituting into our equation and cancelling a factor of we are left with . This implies that must divide and therefore and . The equation now simplifies to and we conclude that the only solution is the pair .