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A122853 Numbers n such that (3^n + 5^n)/8 = A074606(n)/8 is a prime. 31

%I

%S 3,5,7,17,19,109,509,661,709,1231,12889,13043,26723,43963,44789

%N Numbers n such that (3^n + 5^n)/8 = A074606(n)/8 is a prime.

%C (3^n + 5^n)/8 = A074606(n)/8 = A081186(n)/4.

%C Corresponding primes of the form (3^n + 5^n)/2^3 are listed in A121938(n) = A079773(a(n)) = {19,421,10039,95383574161,2384331073699,...}.

%C No other terms less than 100000. - Robert Price, Apr 28 2012

%t Do[f=5^n+3^n;If[PrimeQ[f/2^3],Print[{n,f/2^3}]],{n,1,1231}]

%o (PARI) select(n->isprime((3^n + 5^n)/8), vector(2000,i,i)) \\ _Charles R Greathouse IV_, Feb 13 2011

%Y Cf. A074606, A081186, A121824, A121877, A005058, A005059, A121938, A109347, A079773.

%K more,nonn

%O 1,1

%A _Alexander Adamchuk_, Sep 14 2006

%E a(11)-a(15) from _Robert Price_, Apr 28 2012

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Last modified August 11 00:32 EDT 2020. Contains 336403 sequences. (Running on oeis4.)