Hey I'm stuck on this question on how to prove it, I can prove if it's divisible by 4 but I'm unsure how to do it for 8.
Question
Prove or disprove the following:
If n is an odd integer then n2−1 is divisible by 8 (and 16 is the next question).
Note
I know they're true and false respectively but I'm not sure how to prove it, if you could show me how to do both that would be greatly appreciated!
Working
n∈Zodd⟹n=2k+1 for some k∈Z
∴
= 4k^2+4k+1-1
=4k^2+4k
4(k^2+k)
Since 4|8 \implies 4(k^2+k)|8
\therefore (n^2-1)|8
QED
As you can see from the proof I can easily show that (n^2-1)|4 however I'm not sure what to do after it, as 4\nmid 8 (I'm pretty sure)
Thanks!
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