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 A073723 #16 Mar 18 2025 07:28:59
%S A073723 4,9,16,64,69,218,592,808,910,1921,1957,2648,2860,7609,13462,14953,
%T A073723 16838,20688,27050,44471,80440,91860,122351,131095,154606,166121,
%U A073723 171396,226831,257467,318016,614626,726560,1225277,1366686,1465910,1508284,1790754,1816934,1873100
%N A073723 Numbers k such that sigma(k) mod pi(k) = 1.
%H A073723 Amiram Eldar, <a href="/A073723/b073723.txt">Table of n, a(n) for n = 1..100</a>
%t A073723 Do[s=Mod[DivisorSigma[1, n], PrimePi[n]]; If[s==1, Print[n]], {n, 1, 1000000}]
%o A073723 (PARI) isok(k) = k > 1 && sigma(k) % primepi(k) == 1 \\ _Andrew Howroyd_, Dec 12 2024
%o A073723 (PARI) list(lim) = {my(i = 1, p = 2); forprime(q = 3, lim, for(k = p, q-1, if(sigma(k) % i == 1, print1(k, ", "))); i++; p = q);} \\ _Amiram Eldar_, Mar 18 2025
%Y A073723 Cf. A000203 (sigma), A000720 (pi), A072548.
%K A073723 nonn
%O A073723 1,1
%A A073723 _Labos Elemer_, Aug 05 2002
%E A073723 More terms from _Amiram Eldar_, Mar 18 2025