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 A097645 #19 Jul 11 2025 08:46:46
%S A097645 1,6,54,78,1296,1482,6480,6552,14040,20160,36936,1273896
%N A097645 Numbers k such that k = sigma(phi(k) + pi(k)).
%C A097645 Does this sequence have any odd terms > 1? There is no other term up to 3*10^7.
%C A097645 a(13) > 10350781218. - _J.W.L. (Jan) Eerland_, Dec 25 2021
%e A097645 1273896 is in the sequence because pi(1273896) = 98190, phi(1273896) = 391680, and sigma(98190+391680) = 1273896.
%t A097645 Do[If[n==DivisorSigma[1, EulerPhi[n]+PrimePi[n]], Print[n]], {n, 10000000}]
%t A097645 n=1;Monitor[Parallelize[While[True,If[DivisorSigma[1,EulerPhi[n]+PrimePi[n]]==n,Print[n]];n++];n],n] (* _J.W.L. (Jan) Eerland_, Dec 25 2021 *)
%o A097645 (PARI) isok(k) = k == sigma(eulerphi(k) + primepi(k)); \\ _Michel Marcus_, Dec 25 2021
%Y A097645 Cf. A018784, A082515, A097646.
%K A097645 nonn,more,hard
%O A097645 1,2
%A A097645 _Farideh Firoozbakht_, Sep 07 2004