Giuga Numbers and the arithmetic derivative
  We characterize Giuga Numbers as solutions to the equation $n'=an+1$, with $a \in \mathbb{N}$ and $n'$ being the arithmetic derivative. Although this fact does not refute Lava's conjecture, it brings doubts about its veracity. 
Jos\'e Mar\'ia Grau and Antonio M. Oller-Marc\'en
math.NT