is $\displaystyle \sum_{n=1}^{p-1}{n}$ always divisible by p if p is prime?
Thanks for any help
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is $\displaystyle \sum_{n=1}^{p-1}{n}$ always divisible by p if p is prime?
Thanks for any help
$\displaystyle \sum_{n=1}^{p-1}{n}=\frac{p-1}{2}*p$ as p-1 is even (so divisible by 2) then it is divisible by p?
Exactly. Writing the sum as I did above, you immediately get what you have just written.