## pseudoprimeA number that passes the test of Fermat's little theorem (FLT) for prime numbers but actually isn't a prime. FLT says that if p is prime and a
is coprime to p, then a^{p-1}
- 1 is divisible by p. If a number x is not prime, a
is coprime to x, and x divides a^{x-1}
- 1, then x is called a pseudoprime to base a. A number x that is a pseudoprime for all values of a that
are coprime to x is called a Carmichael
number. The smallest pseudoprime for in base 2 is 341. It isn't prime
because 341 = 11 × 31; however, it satisfies FLT: 2^{340} -
1 is divisible by 341. ## Related categories• PRIME NUMBERS• TYPES OF NUMBER | |||||

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