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 A296214 #11 Nov 15 2024 06:59:54 %S A296214 2,4,6,8,9,10,12,14,16,18,20,21,22,24,26,27,28,30,32,33,34,36,38,39, %T A296214 40,42,44,45,46,48,49,50,52,54,55,56,57,58,60,62,63,64,66,68,70,72,74, %U A296214 75,76,77,78,80,82,84,86,88,90,91,92,93,94,95,96,98,99,100,102,104,105,106,108,110,111,112,114,115 %N A296214 Numbers k for which there is at least one x < k such that phi(x) = phi(k). %C A296214 Numbers k for which A081373(k) > 1. %C A296214 Apart from the initial term 2, this is the complement of union of A000040 (primes) and A069823. %H A296214 Antti Karttunen, <a href="/A296214/b296214.txt">Table of n, a(n) for n = 1..12973</a> %H A296214 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp). %o A296214 (PARI) for(n=1,200,y=0;s=eulerphi(n);for(k=1,(n-1),if(eulerphi(k)==s,y=1;break)); if(y,print1(n,","))); %o A296214 (PARI) is(k) = invphiMin(eulerphi(k)) < k; \\ _Amiram Eldar_, Nov 15 2024, using _Max Alekseyev_'s invphi.gp %Y A296214 Cf. A000010, A069822, A069823, A081373. %Y A296214 Cf. A296087 (a subsequence). %K A296214 nonn %O A296214 1,1 %A A296214 _Antti Karttunen_, Dec 08 2017