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 A368651 #24 Aug 20 2024 16:01:24
%S A368651 3,5,17,49,53,185,503,1301,1689,1797,5929,14747,20433,29903,42137,
%T A368651 64763
%N A368651 Numbers k such that 2^sigma(k) - k is a prime.
%C A368651 If it exists, a(17) > 120000. - _Michael S. Branicky_, Aug 19 2024
%e A368651 5 is in the sequence because 2^sigma(5)-5 = 2^6-5 = 59 is prime.
%t A368651 a[n_] := Select[Range@ n, PrimeQ[2^DivisorSigma[1, #] - #] &]; a[20000]
%t A368651 DeleteCases[ParallelTable[If[PrimeQ[2^DivisorSigma[1,k]-k],k,n],{k,1,10^4}],n]
%o A368651 (Magma) [n: n in[1..10000] | IsPrime((2^SumOfDivisors(n)) - n)];
%Y A368651 Cf. A000043, A000203, A000668, A023194, A023195, A253850, A253851.
%K A368651 nonn,more
%O A368651 1,1
%A A368651 _J.W.L. (Jan) Eerland_, Jan 02 2024
%E A368651 a(16) from _J.W.L. (Jan) Eerland_, Jan 25 2024