• Nov 4th 2008, 10:46 AM
tret
Given that if n is a product of twin primes, say n = p(p+2), then
φ(n)σ(n)=(n+1)(n-3)
• Nov 4th 2008, 11:02 AM
ThePerfectHacker
Quote:

Originally Posted by tret
Given that if n is a product of twin primes, say n = p(p+2), then
φ(n)σ(n)=(n+1)(n-3)

$\phi(p(p+2)) = \phi (p)\phi(p+2)$
$\sigma(p(p+2)) = \sigma (p) \sigma (p+2)$

Now use fact that $\phi (q) = q-1, \sigma(q) = q+1$ where $q$ is prime.