1.Previous
3.Next

is the smallest pseudoprime base 2 (see Figure 1 of).

There are only 21853 pseudoprimes base 2 that are less than 2.5 (see page 1005 of ). This means that, for n up to 2.5, if 2^n-1 (modulo n) equals 1, then n is prime, unless n is one of these 21853 pseudoprimes.

Some composite numbers (Carmichael numbers) have the property that a^{n - 1} is 1 (modulo n) for every a that is coprime to n. The smallest example is n = 561 = 3·11·17, for which a⁵⁶⁰

1.Previous
3.Next