Giuga number

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Definition

A composite number is termed a Giuga number if and only if it satisfies the following equivalent conditions:

  1. For every prime number dividing , we have that divides , or equivalently, that divides .
  2. We have the following congruence:

where denotes the Euler totient function of .

Note that all prime numbers satisfy the stated condition but we deliberately exclude them by imposing the restriction of being composite.

Facts

Occurrence

Initial examples

30, 858, 1722, 66198, [SHOW MORE]View list on OEIS