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 A383220 #12 May 01 2025 21:54:10
%S A383220 1,2,3,5,6,11,14,15,20,21,23,24,26,29,30,33,35,39,41,44,51,53,65,68,
%T A383220 69,74,78,83,86,88,89,90,95,105,111,113,114,116,117,119,125,126,131,
%U A383220 134,135,138,140,141,146,147,153,155,156,158,165,168,171,173,174,179
%N A383220 Integers k such that rad(k)*2^(k/rad(k)) + 1 is prime where rad = A007947.
%e A383220 20 is a term because 10*2^(20/10) + 1 = 41 is prime, where 10 is largest squarefree divisor of k = 20.
%t A383220 s={};Do[r=Last[Select[Divisors[n], SquareFreeQ]];If[PrimeQ[r*2^(n/r)+1],AppendTo[s,n]],{n,179}];s (* _James C. McMahon_, May 01 2025~ *)
%o A383220 (Magma) [k: k in [1..180] | IsPrime(&*PrimeDivisors(k)*2^(k div &*PrimeDivisors(k))+1)];
%o A383220 (PARI) isok(k) = my(r=factorback(factorint(k)[, 1])); ispseudoprime(r*2^(k/r) + 1); \\ _Michel Marcus_, Apr 20 2025
%Y A383220 Supersequence of A005384.
%Y A383220 Cf. A002234, A003557, A007947.
%K A383220 nonn
%O A383220 1,2
%A A383220 _Juri-Stepan Gerasimov_, Apr 19 2025