# Fermat's Little Theorem

• October 19th 2009, 04:07 PM
kyldn6
Fermat's Little Theorem
Prove that $12\ |\ n^2-1$ if g.c.d. (n,6) = 1.
• October 19th 2009, 07:32 PM
chisigma
If g.c.d. (n,6) = 1 that means that $2 \nmid n$ and $3 \nmid n$, i.e. n is and odd number non multiple of 3. But if $2 \nmid n$ and $3 \nmid n$ means also that $n-1$ and $n+1$ are both even numbers and 3 devides one of them. The conclusion is that...

$2\cdot 2\cdot 3 \mid (n+1)\cdot (n-1)$

Kind regards

$\chi$ $\sigma$
• October 19th 2009, 09:47 PM
tonio
Quote:

Originally Posted by chisigma
If g.c.d. (n,6) = 1 that means that $2 \nmid n$ and $3 \nmid n$,

i.e. n is and odd number non multiple of 3. But if $2 \nmid n$ and $3 \nmid n$ means also that $n-1$ and $n+1$ are both even numbers and 3 devides one of them. The conclusion is that...

$2\cdot 2\cdot 3 \mid (n+1)\cdot (n-1)$

Kind regards

$\chi$ $\sigma$

.