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A082387
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Numbers k such that (5^k + 2^k)/7 is prime.
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25
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3, 17, 19, 47, 101, 1709, 2539, 5591, 6037, 8011, 19373, 26489, 27427
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OFFSET
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1,1
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COMMENTS
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No other terms less than 100000. - Robert Price, Apr 17 2012
Some of the results were computed using the PrimeFormGW (PFGW) primality-testing program. - Hugo Pfoertner, Nov 14 2019
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LINKS
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EXAMPLE
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a(1)=3 because (5^3 + 2^3)/7 = (125 + 8)/7 = 19 is prime.
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MATHEMATICA
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Do[f=(2^n+5^n)/7; If[PrimeQ[f], Print[{n, f}]], {n, 1, 35000}] (* Alexander Adamchuk, Feb 06 2007 *)
Select[Range[0, 10000], PrimeQ[(5^# + 2^#)/7] &] (* G. C. Greubel, Nov 02 2018 *)
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PROG
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(Magma) [n : n in [1..10000] | IsPrime((5^n+2^n) div 7)]; // G. C. Greubel, Nov 02 2018
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CROSSREFS
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Cf. A057469 ((2^k + 3^k)/5 is prime).
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KEYWORD
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more,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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