Prime Curios!: 561

561
(another Prime Pages' Curiosity)

Curios:

Curios Search:
Participate:

GIMPS has discovered a new largest known prime number: 2^82589933-1 (24,862,048 digits)

561 is the smallest Carmichael number.

561² ± 2 are two consecutive primes. [Luhn]

The sum of the squares of the first five non-squarefree numbers. [Post]

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