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 A377927 #11 Nov 14 2024 08:23:32
%S A377927 1,5,17,57,675,1329,1425,3803,39617
%N A377927 Numbers k such that 4^sigma(k) - k is a prime.
%e A377927 17 is in the sequence because 4^sigma(17) - 17 = 4^18 - 17 = 68719476719 is prime.
%t A377927 a[n_] := Select[Range@ n, PrimeQ[4^DivisorSigma[1, #] - #] &]; a[20000]
%t A377927 DeleteCases[ParallelTable[If[PrimeQ[4^DivisorSigma[1,k]-k],k,n],{k,1,10^4}],n]
%o A377927 (Magma) [n: n in[1..10000] | IsPrime((4^SumOfDivisors(n)) - n)];
%Y A377927 Cf. A000043, A000203, A000668, A023194, A023195, A253850, A253851, A368651, A367460.
%K A377927 nonn,more
%O A377927 1,2
%A A377927 _J.W.L. (Jan) Eerland_, Nov 11 2024
%E A377927 a(9) from _Michael S. Branicky_, Nov 11 2024