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Question Number 211443 by BaliramKumar last updated on 09/Sep/24

Answered by A5T last updated on 09/Sep/24

Note that n≤10 and cannot be composite ⇒It remains to check for n=2,3,5,7 2^2 −1=3;2^3 −1=7;2^5 −1=31;2^7 −1=127 ⇒only 4 are prime

$${Note}\:{that}\:{n}\leqslant\mathrm{10}\:{and}\:{cannot}\:{be}\:{composite} \\ $$$$\Rightarrow{It}\:{remains}\:{to}\:{check}\:{for}\:{n}=\mathrm{2},\mathrm{3},\mathrm{5},\mathrm{7} \\ $$$$\mathrm{2}^{\mathrm{2}} −\mathrm{1}=\mathrm{3};\mathrm{2}^{\mathrm{3}} −\mathrm{1}=\mathrm{7};\mathrm{2}^{\mathrm{5}} −\mathrm{1}=\mathrm{31};\mathrm{2}^{\mathrm{7}} −\mathrm{1}=\mathrm{127} \\ $$$$\Rightarrow{only}\:\mathrm{4}\:{are}\:{prime} \\ $$

Commented by BaliramKumar last updated on 09/Sep/24

thanks

$${thanks} \\ $$

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