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 A373435 #82 Jan 05 2025 13:36:15 %S A373435 4,48,72,432,1728,10368,184320,1658880,6220800,10222080,12856320000 %N A373435 Iterate the function x <- phi(sigma(x)). The sequence lists the smaller member of cycles of length 2. %C A373435 A cycle of length 2 also starts at 3852635996160. 3852635996160, 4869303828480, and 23971865863680 are also terms in the sequence. The sequence is complete through 10^13. - _Jud McCranie_, Sep 14 2024 %C A373435 166144927334400, 273145872384000, 1904394240000000,2779315686604800, 3644668394864640, 32729712349340160, 48693038284800000, 86790832128000000, 382404221337600000, 2684203735449600000, 5246585916751872000, 6169596402106368000, 13477567109529600000, 22998695842676736000, 38039819551128944640, 90555444080640000000, 102336861080974786560, 130026464870400000000, 222489728778240000000, 499064687988572160000, 2927044657152000000000, 19697331219625672704000, 23473340597403648000000, 73262977439150112768000, 1362680919097344000000000, 14128156119169341849600000, 16615689577928023080960000, 53129683677797469388800000, 6512790537509850316800000000, 125020570798295875584000000000, 201603700212193346715648000000, 1622429777898127409283072000000, 2631371767787268127693209600000, 71803515676046099742720000000000, 105852742809627160240717824000000000, 5528044915051901005564508897280000000, 15042880212263420006968149934080000000, 2013381648407800940932784726212608000000, 67868597277402193009117012867153920000000, 17285817653863442809402049534361600000000000 are also in this sequence. - _Richard R. Forberg_, Oct 27 2024 %e A373435 phi(sigma(4)) = 6 and phi(sigma(6)) = 4, so 4 (the smallest term) is in the sequence. %t A373435 Select[Range[10^6], # == EulerPhi[DivisorSigma[1,EulerPhi[DivisorSigma[1,#]]]] && # < EulerPhi[DivisorSigma[1,#]]&] (* _Stefano Spezia_, Jun 07 2024 *) %o A373435 (PARI) isok(x) = my(y = eulerphi(sigma(x))); if (y > x, x == eulerphi(sigma(y))); \\ _Michel Marcus_, Jun 06 2024 %Y A373435 Subsequence of A067883 and A376256. %Y A373435 Cf. A000010, A000203, A062401, A001229, A095955, A095956, A373453, A373454. %K A373435 nonn,more %O A373435 1,1 %A A373435 _Jud McCranie_, Jun 06 2024