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 A066950 #19 Sep 04 2022 21:03:55 %S A066950 1,11,18,75,172,372,482,732,3276,7965,13068,46476,103488,252240, %T A066950 727956,1795605,6030528,8769600,15436092,56747712,224518995,297780084, %U A066950 317961000,855489144,2691137721,58016937600,127198874880,228517311456,411814778112 %N A066950 Numbers k such that phi(sigma(k)) + sigma(phi(k)) = 2k. %C A066950 a(26) > 3*10^10. - _Donovan Johnson_, Mar 05 2014 %e A066950 phi(sigma(11)) + sigma(phi(11)) = phi(12) + sigma(10) = 4 + 18 = 2*11, so 11 is in the sequence. %t A066950 f[n_] := EulerPhi[DivisorSigma[1, n]]+DivisorSigma[1, EulerPhi[n]]; Select[Range[1, 10^5], f[ # ]==2*#&] %Y A066950 Cf. A000010, A000203. %K A066950 more,nonn %O A066950 1,2 %A A066950 _Joseph L. Pe_, Jan 25 2002 %E A066950 Edited by _Dean Hickerson_, Jan 26 2002 %E A066950 a(20)-a(25) from _Donovan Johnson_, Sep 16 2009 %E A066950 a(26)-a(28) from _Kevin P. Thompson_, Apr 19 2022 %E A066950 a(29) from _Kevin P. Thompson_, Sep 04 2022