Carmichael function

The Carmichael function, denoted as \( \lambda(n) \), is a function that gives the least positive integer \( m \) such that \( a^m \equiv 1 \pmod{n} \) for all integers \( a \) that are coprime to \( n \). In other words, it is the smallest exponent for which every number coprime to \( n \) has a power that is congruent to 1 modulo \( n \).