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 A057826 #11 Nov 11 2024 05:20:27
%S A057826 6,12,18,30,22,42,0,60,54,66,46,90,0,58,62,120,0,126,0,150,98,138,94,
%T A057826 210,0,106,162,174,118,198,0,240,134,0,142,270,0,0,158,330,166,294,0,
%U A057826 276,0,282,0,420,0,250,206,318,214,378,242,348,0,354,0,462,0,0,254,510
%N A057826 Greatest number with totient 2n (or zero when no such number exists).
%C A057826 If a(n) = 0, n is a nontotient number - see (A005277)/2.
%H A057826 T. D. Noe, <a href="/A057826/b057826.txt">Table of n, a(n) for n=1..10000</a>
%H A057826 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp).
%t A057826 a = Table[0, {100}]; Do[ t = EulerPhi[n]/2; If[t < 101, a[[t]] = n], {n, 1, 10^3}]; a
%o A057826 (PARI) a(n) = invphiMax(2*n); \\ _Amiram Eldar_, Nov 11 2024, using _Max Alekseyev_'s invphi.gp
%Y A057826 Bisection of A057635. Cf. A000010, A005277, A002181.
%K A057826 nonn
%O A057826 1,1
%A A057826 _Robert G. Wilson v_, Nov 08 2000