Prime Curios!: 561

561
(another Prime Pages' Curiosity)

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561 is the smallest Carmichael number.

561² ± 2 are two consecutive primes. [Luhn]

561 is the sum of the squares of the first five not square-free numbers. [Post]

(There is one curio for this number that has not yet been approved by an editor.)

To link to this page use http://primes.utm.edu/curios/page.php?number_id=65