
With numbers as small as 2⁻¹²², consider what may seem impossibly unlikely - bemmu
https://blogs.msdn.microsoft.com/oldnewthing/20160114-00/?p=92851
======
brudgers
_Numbers that fool the Fermat test are called Carmichael numbers, and little
is known about them other than that they are extremely rare. There are 255
Carmichael numbers below 100,000,000. The smallest few are 561, 1105, 1729,
2465, 2821, and 6601. In testing primality of very large numbers chosen at
random, the chance of stumbling upon a value that fools the Fermat test is
less than the chance that cosmic radiation will cause the computer to make an
error in carrying out a ``correct '' algorithm. Considering an algorithm to be
inadequate for the first reason but not for the second illustrates the
difference between mathematics and engineering._ \-- SICP

[https://github.com/ikr/sicp/blob/master/exercises/chapter_1/...](https://github.com/ikr/sicp/blob/master/exercises/chapter_1/1.27.scm)

