i still do not get it. so if n=4^x(8k+7), we need to show that n+1 or n+2 is not of that form. how do we show that?
i'm wondering from the link, when we consider n = 8k+7 then n is congruent to 7 mod 8 but if n =4^x(8k+7) then n is congruent to 0 mod 8 if x>3 right? yet why does it say that it cant be a sum of three squares if n = 8k+7 and n =4^x(8k+7)?