Prime or not?
(All calculations are in base 10.)
Consider the number , where and are distinct digits between and inclusive.
Is this number prime?
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1 solution
A number is divisible by 11 if you alternately add and subtract the digits and get a sum of 0.
1 − A + B − B + A − 1 = 0
So the number is divisible by 11, and thus not prime.