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 A053568 #21 Jun 15 2024 05:48:43 %S A053568 2,4,6,6,10,12,6,8,16,18,12,22,20,12,18,28,30,20,16,24,36,18,24,40,42, %T A053568 24,46,42,20,32,52,40,36,58,60,30,36,48,66,32,44,70,72,36,40,36,60,78, %U A053568 54,82,64,42,56,88,24,72,60,46,72,96,42,60,100,102,48,106 %N A053568 Totients of nontotient numbers. %C A053568 See comment at analogous sequence A053474. %H A053568 Amiram Eldar, <a href="/A053568/b053568.txt">Table of n, a(n) for n = 1..10000</a> %F A053568 a(n) = A000010(A007617(n)). %e A053568 If k = 19 then there is no number x such that phi(x) = k exists; however, phi(19) = 18. %e A053568 k = 27 is also a nontotient number whose totient is 18. %o A053568 (PARI) lista(nn) = for (n=1, nn, if (!istotient(n), print1(eulerphi(n), ", "))); \\ _Michel Marcus_, Nov 20 2017 %Y A053568 Cf. A000010, A007617, A053474. %K A053568 nonn %O A053568 1,1 %A A053568 _Labos Elemer_, Jan 17 2000