Find the sum of all positive integers which can be expressed as $\sqrt{7p^n+9}$ for some positive integer $n$ and some prime number $p$.
Official answer 49, my answer 10+11+24=45. Is it wrong ?
Sum of all positive integers : $\sqrt{7p^n+9}$
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number-theory
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2Indeed, $45\ne49$. – 2017-01-28
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2I think they have also added $\sqrt {7 (1)^n +9} =4$, but clearly $1$ is not prime. – 2017-01-28
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0@ Rohan, I think so. Thank you both. – 2017-01-28
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2I think, they knew that $p=1$ was not prime, and included $n=0$ (for some "non-negative integer", instead of "positive" integer). – 2017-01-28
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0@Dietrich Burde, you're right. Thank you. – 2017-01-28