σ is an odd integer if and only if n is a perfecdt square or twice a perfect square. [Hint: If p i s an odd prime, then 1+p+p^2+...+p^k is odd only when k is even]
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Could you please explain the link between σ, and ? I take that σ is the sum of the divisors of , is that right ?
Originally Posted by MichaelG σ is an odd integer if and only if n is a perfecdt square or twice a perfect square. [Hint: If p i s an odd prime, then 1+p+p^2+...+p^k is odd only when k is even] It is a basic fact that if is the prime decomposition of a natural number, then Well, now just use the hint... Tonio
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