

A082387


Numbers k such that (5^k + 2^k)/7 is prime.


25



3, 17, 19, 47, 101, 1709, 2539, 5591, 6037, 8011, 19373, 26489, 27427
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OFFSET

1,1


COMMENTS

No other terms less than 100000.  Robert Price, Apr 17 2012
Some of the results were computed using the PrimeFormGW (PFGW) primalitytesting program.  Hugo Pfoertner, Nov 14 2019


LINKS



EXAMPLE

a(1)=3 because (5^3 + 2^3)/7 = (125 + 8)/7 = 19 is prime.


MATHEMATICA

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 *)


PROG

(Magma) [n : n in [1..10000]  IsPrime((5^n+2^n) div 7)]; // G. C. Greubel, Nov 02 2018


CROSSREFS

Cf. A057469 ((2^k + 3^k)/5 is prime).


KEYWORD

more,nonn


AUTHOR



EXTENSIONS



STATUS

approved



