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%I A125956 #18 Sep 19 2024 04:18:17
%S A125956 3,7,127,283,883,1523,4001
%N A125956 Numbers k such that (2^k + 9^k)/11 is prime.
%C A125956 All terms are primes. Note that first 3 terms {3, 7, 127} are primes of the form 2^q - 1, where q = {2, 3, 7} is prime too. Corresponding primes of the form (2^k + 9^k)/11 are {67, 434827, ...}.
%C A125956 a(8) > 10^5. - _Robert Price_, Dec 23 2012
%t A125956 Do[p=Prime[n];f=(2^p+9^p)/11; If[PrimeQ[f], Print[{p, f}]], {n, 1, 100}]
%o A125956 (PARI) is(n)=ispseudoprime((2^n+9^n)/11) \\ _Charles R Greathouse IV_, Feb 20 2017
%Y A125956 Cf. A000978 = numbers n such that (2^n + 1)/3 is prime.
%Y A125956 Cf. A057469 = numbers n such that (2^n + 3^n)/5 is prime.
%Y A125956 Cf. A082387 = numbers n such that (2^n + 5^n)/7 is prime.
%K A125956 hard,more,nonn
%O A125956 1,1
%A A125956 _Alexander Adamchuk_, Feb 06 2007
%E A125956 2 more terms from _Rick L. Shepherd_, Feb 14 2007
%E A125956 a(7) from _Robert Price_, Dec 23 2012

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