prime cirterion, \phi (n) divides (n - 1) and (n + 1) divides \sigma (n)
Source: Indian Postal Coaching 2008 set 4 p2
May 25, 2020
number theoryprimesprimeprime numbersdivides
Problem Statement
Prove that an integer is a prime if and only if divides and divides . [Here is the Totient function and is the divisor - sum function.] is squarefree