Determine all pairs of natural numbers that satisfy and .
Solutions — 2
Solution 1
As and , at least one of the numbers and is divisible by . Since , the other one must also be divisible by . Both and are divisors of . All divisors of that are divisible by are , , and . The only two of these with difference are and . A straightforward check shows that indeed.
Solution 2
As , both and are divisors of . All divisors of are
1, 2, 4, 8, 11, 22, 23, 44, 46, 88, 92, 184, 253, 506, 1012, 2024.
As , we must have . This observation cuts out all cases except and . As differences between , , and are larger than , it suffices to check the options and which imply and , respectively. As , the only solution can be . An easy check shows that indeed.
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