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 A377786 #43 Nov 14 2024 08:23:35
%S A377786 4,524,7206,11156
%N A377786 Numbers k such that 5^sigma(k) - k is a prime.
%e A377786 4 is in the sequence because 5^sigma(4) - 4 = 5^7 - 4 = 78121 is prime.
%t A377786 a[n_] := Select[Range@ n, PrimeQ[5^DivisorSigma[1, #] - #] &]; a[20000]
%t A377786 DeleteCases[ParallelTable[If[PrimeQ[5^DivisorSigma[1,k]-k],k,n],{k,1,10^4}],n]
%o A377786 (Magma) [n: n in[1..10000] | IsPrime((5^SumOfDivisors(n)) - n)];
%Y A377786 Cf. A000043, A000203, A000668, A023194, A023195, A253850, A253851, A368651, A367460, A377927.
%K A377786 nonn,more
%O A377786 1,1
%A A377786 _J.W.L. (Jan) Eerland_, Nov 11 2024
%E A377786 a(4) from _Michael S. Branicky_, Nov 11 2024