Optimus Prime

Find all n n such that n 2 2 2014 × 2014 n + 4 2013 ( 201 4 2 1 ) n^{2} - 2^{2014}\times 2014n + 4^{2013} (2014^{2}-1) is prime, where n n is a positive integer.

10 8 2 No positive integer exist 1 34 Infinitely Many 6

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1 solution

Mark Hennings
Jun 29, 2017

Since N = n 2 2 2014 × 2014 n + 4 2013 ( 201 4 2 1 ) = ( n 2 2013 × 2014 ) 2 4 2013 = ( n 2 2013 × 2013 ) ( n 2 2013 × 2015 ) N \; = \; n^2 - 2^{2014} \times 2014n + 4^{2013}(2014^2-1) \; = \;\big(n - 2^{2013}\times2014\big)^2 - 4^{2013} \; = \; \big(n - 2^{2013}\times2013\big)\big(n - 2^{2013}\times2015\big) the only way that N N can be prime is if one of these factors is ± 1 \pm1 , and hence n n is one of 2 2013 × 2013 + 1 2 2013 × 2013 1 2 2013 × 2015 + 1 2 2013 × 2015 1 2^{2013}\times2013 + 1 \hspace{1cm} 2^{2013}\times2013-1 \hspace{1cm} 2^{2013}\times2015+1 \hspace{1cm} 2^{2013}\times2015-1 The corresponding value of N N in each of these cases is 1 2 2014 1 2 2014 2 2014 + 1 2 2014 1 1 - 2^{2014} \hspace{2cm} -1 - 2^{2014} \hspace{2cm} 2^{2014} + 1 \hspace{1cm} 2^{2014} - 1 respectively. But 3 = 2 2 1 3 = 2^2 - 1 divides 2 2014 1 2^{2014}-1 , while 5 = 2 2 + 1 5 = 2^2 + 1 divides 2 2014 + 1 2^{2014} + 1 . Thus no integer value of n n exists that makes N N prime.

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