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 A378512 #8 Dec 21 2024 00:49:04
%S A378512 1,7,13,77,395,2867,3959,5023
%N A378512 Numbers k such that 6^sigma(k) - k is a prime.
%C A378512 a(9) > 10^5. - _Michael S. Branicky_, Dec 01 2024
%e A378512 7 is in the sequence because 6^sigma(7) - 7 = 6^8 - 7 = 1679609 is prime.
%t A378512 a[n_] := Select[Range@ n, PrimeQ[6^DivisorSigma[1, #] - #] &]; a[20000]
%t A378512 DeleteCases[ParallelTable[If[PrimeQ[6^DivisorSigma[1,k]-k],k,n],{k,1,10^4}],n]
%o A378512 (Magma) [n: n in[1..10000] | IsPrime((6^SumOfDivisors(n)) - n)];
%o A378512 (PARI) isok(k) = ispseudoprime(6^sigma(k) - k); \\ _Michel Marcus_, Dec 09 2024
%Y A378512 Cf. A000043, A000203, A000668, A023194, A023195, A253850, A253851, A368651, A367460, A377927, A377786.
%K A378512 nonn,more
%O A378512 1,2
%A A378512 _J.W.L. (Jan) Eerland_, Nov 29 2024