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Problem 35


Problem 35


Circular primes

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.

How many circular primes are there below one million?


圆周素数

197被称为圆周素数,因为将它逐位旋转所得到的数:197/971和719都是素数。

小于100的圆周素数有十三个:2、3、5、7、11、13、17、31、37、71、73、79和97。

小于一百万的圆周素数有多少个?