Poulet number

Definition

A Poulet number or Sarrus number is an odd composite number $n$ such that:

$2^{n-1}\equiv 1\mod n$.

In other words, $n$ divides $2^{n-1}-1$. Equivalently, $n$ is a Fermat pseudoprime modulo $2$.

Relation with other properties

Stronger properties

• Absolute pseudoprime (at least, in the odd number case).