An integer N which is a product of distinct primes and which satisfies 1/N + sum_(p|N) 1/p = 1 . The first few are 2, 6, 42, 1806, 47058, ... (OEIS A054377). The similar equation -1/N + sum_(p|N) 1/p = 1 arises in the definition of Giuga numbers.

Giuga number | pseudoperfect number