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 A353679 #7 May 06 2022 18:27:51 %S A353679 1,3,15,39,45,111,117,175,183,195,219,333,357,471,549,555,579,585,657, %T A353679 831,915,939,1071,1095,1191,1263,1371,1413,1443,1623,1665,1737,1839, %U A353679 1983,2019,2199,2271,2275,2295,2355,2379,2493,2631,2745,2817,2847,2895,2991,3279,3285,3459,3573,3603,3639,3711,3789,3963 %N A353679 Odd numbers k for which phi(k) = phi(sigma(k)). %H A353679 <a href="/index/O#opnseqs">Index entries for sequences where odd perfect numbers must occur, if they exist at all</a> %H A353679 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a> %t A353679 Select[Range[1, 4000, 2], EulerPhi[#] == EulerPhi[DivisorSigma[1, #]] &] (* _Amiram Eldar_, May 06 2022 *) %o A353679 (PARI) %o A353679 A353680(n) = ((n%2) && (eulerphi(sigma(n))==eulerphi(n))); %o A353679 isA353679(n) = A353680(n); %Y A353679 Odd terms in A006872. %Y A353679 Cf. A000010, A000035, A000203, A062401, A353637, A353680 (characteristic function). %K A353679 nonn %O A353679 1,2 %A A353679 _Antti Karttunen_, May 06 2022