Problem 1095. Circular Primes (based on Project Euler, problem 35)

Created by James

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The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, are themselves prime.

There are thirteen such primes below 100: 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, 79, and 97.

Given a number x, write a MATLAB script that will tell you the number of circular primes less than or equal to x as well as a sorted list of what the circular prime numbers are.

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Last Solution submitted on Apr 04, 2024

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Ryan on 5 Dec 2012

Very nice problem!

Christopher on 5 Dec 2012

How do you return two separable outputs via a single vector?

James on 6 Dec 2012

Christopher, I should have been more clear in the problem description.

There are two outputs to the function. The first output (how_many) is a scalar, and is the number of circular primes.

The second output (what_numbers) is the vector containing the values of the circular primes.

Does this help?

Christopher on 18 Dec 2012

197 is not circular prime, because neither 791 nor 917 are themselves prime. Only test case 2 is correct.

James on 19 Dec 2012

Christopher, if our number is represented as ABC, then a cicrular prime is a number where ABC, BCA, and CAB are all prime. You are either shifting the numbers in the opposite direction or scrambling them. Not every permutation of the numbers has to be a prime number, although that in itself would be an interesting Cody problem. :-)

Bùi Dương on 3 Dec 2023

good question! tricky

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