|
%I #15 Nov 26 2022 16:56:24
%S 3,5,7,17,19,109,509,661,709,1231,12889,13043,26723,43963,44789
%N Numbers k such that (3^k + 5^k)/8 = A074606(k)/8 is a prime.
%C (3^k + 5^k)/8 = A074606(k)/8 = A081186(k)/4.
%C Corresponding primes of the form (3^k + 5^k)/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 nonn,more
%O 1,1
%A _Alexander Adamchuk_, Sep 14 2006
%E a(11)-a(15) from _Robert Price_, Apr 28 2012
|
