31172165

This number is a composite.

10223*2^31172165 + 1 is a 9383761-digit proven prime . It is neither the largest known prime nor a self number. BUT, 10223*2^31172165 + 1 is the largest known prime P such that the repunit number ( 10^P - 1)/9 is a self number (!), as of July 4 , 2019. [Kontobesar]