Knödel number

In number theory, an n-Knödel number for a given positive integer n is a composite number m with the property that each i < m coprime to m satisfies i m − n ≡ 1 ( mod m ) . The concept is named after Walter Knödel.

The set of all n-Knödel numbers is denoted K_n. The special case K₁ represents the Carmichael numbers.

Every composite number m is a n-Knödel number for n = m − φ ( m ) .