I couldn't find any relations inbetween those circles, the only one are 18 x 4 equals 72, and 19 x 2 equals 38, but I don't see any pattern at all. Tried adding them up, multiplying them, but still can't find any pattern. Can I have a hint?
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$\begingroup$I may have "a" solution but I doubt that it is "the" solution.
In the first circle, $18$ has the divisors $1,2,3,6,9,18$ while $19$ has divisors $1,19$. There are $7$ unique divisors overall and so the number on the top is $7 \times 1=7$.
In the second circle, $38$ has the divisors $1,2,19,38$ while $43$ has divisors $1,43$. There are $5$ unique divisors overall and so the number on the top is $5 \times 2=10$.
In the third circle, $125$ has the divisors $1,5,25,125$ while $72$ has divisors $1,2,3,4,6,8,9,12,18,24,36,72$. There are $15$ unique divisors overall and so the number on the top is $15 \times 3=45$.
As you can see, it sort of makes sense and there is no mathematical error, however I doubt this is the solution. The order of the circles usually doesn't matter.
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