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 A333338 #13 Mar 15 2020 07:54:00 %S A333338 1,7,11891,130801,273493,1438811,3008423,6290339,15826921,33092653, %T A333338 69193729,144677797,174096131,364019183,761131019,1591455767, %U A333338 1915057441,3327589331,4004211013,8372441209,17506013437,21065631851,36603482641,44046321143,76534554613,92096853299 %N A333338 Numbers k such that sigma_2(k) = sigma_2(phi(k)). %C A333338 The sequence is infinite since it contains all the numbers of the form 11^i*23^j*47 for i,j > 0. Up to 10^11 the only terms not of this form are 1 and 7. - _Giovanni Resta_, Mar 15 2020 %e A333338 50 = 1^2 + 7^2 (sum of the squares of the divisors of 7) = 1^2 + 2^2 + 3^2 + 6^2 (sum of the squares of the divisors of 6 = phi(7)). So 7 is in the sequence. %t A333338 Select[Range[10!],DivisorSigma[2,#]==DivisorSigma[2,EulerPhi[#]]&] %o A333338 (PARI) isok(m) = sigma(m, 2) == sigma(eulerphi(m), 2); \\ _Michel Marcus_, Mar 15 2020 %Y A333338 Cf. A000010, A001157, A070418, A033631. %K A333338 nonn %O A333338 1,2 %A A333338 _Ivan N. Ianakiev_, Mar 14 2020 %E A333338 More terms from _Giovanni Resta_, Mar 15 2020