A prime number for which every cyclic rotation of its numerical digits is also a prime number. In decimal representation, is an example because are all prime numbers. A multi-digit circular prime can contain only : any other digit can be rotated into the units position and force divisibility by or .
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A circular prime is a particular type of prime number that remains prime when its digits are rotated in all possible ways. For example, let's consider the prime number 197. Its digit rotations are 197, 971, and 719, and since all of these numbers are prime, 197 is classified as a circular prime. To give another example, the number 13 is a circular prime because its rotations (13 and 31) are both prime numbers.