This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A121938 #10 Aug 28 2025 17:24:13
%S A121938 19,421,10039,95383574161,2384331073699,
%T A121938 1925929944387235853055979210606894889560480247048440342330377620014353281101
%N A121938 Primes of the form (3^k + 5^k)/2^3 = A074606(k)/8.
%C A121938 Corresponding numbers k such that (3^k + 5^k)/8 is prime are listed in A122853. All these numbers are primes. - _Alexander Adamchuk_, Sep 14 2006
%C A121938 The next term is too large to include. - _Alexander Adamchuk_, Sep 14 2006
%F A121938 a(n) = (A122853(n)^3 + A122853(n)^5)/8. a(n) = A074606[A122853(n)]/8 = A081186[A122853(n)]/4. a(n) = A079773[A122853(n)]. - _Alexander Adamchuk_, Sep 14 2006
%t A121938 Do[f=5^n+3^n;If[PrimeQ[f/2^3],Print[{n,f/2^3}]],{n,1,1231}] (* _Alexander Adamchuk_, Sep 14 2006 *)
%Y A121938 Cf. A074706, A122853, A081186, A079773, A121824, A121877, A005058, A005059, A121938, A109347.
%K A121938 nonn,changed
%O A121938 1,1
%A A121938 _Zak Seidov_, Sep 10 2006
%E A121938 More terms from _Alexander Adamchuk_, Sep 14 2006