Emirp primE
Number Theory
Level
1
An emirp is a prime number that is also a prime number when the digits are reversed.
What is the smallest emirp above 50?
The answer is 71.
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1 solution
All two-digit numbers ending with 5 or 6 cannot be a prime number, therefore, all two-digit numbers starting with 5 or 6 cannot be an emirp number. Checking that 70 is not prime, one can immediately find that 71 is prime and so is 17, therefore, 71 is the smallest emirp number more than 50.