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 A081375 #14 Nov 08 2024 07:20:06
%S A081375 1,2,6,12,30,42,72,78,84,90,190,216,222,228,234,252,270,540,546,570,
%T A081375 630,738,744,770,792,858,900,924,930,990,1050,1638,1710,1890,1980,
%U A081375 2100,2310,2418,2442,2508,2562,2574,2604,2700,2772,2790,2850,2970,3150
%N A081375 a(n) is the least number k such that A081373(k) = n.
%H A081375 Amiram Eldar, <a href="/A081375/b081375.txt">Table of n, a(n) for n = 1..1000</a>
%H A081375 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp).
%t A081375 f[x_] := Count[Table[EulerPhi[j]-EulerPhi[x], {j, 1, x}], 0] t=Table[0, {50}]; Do[s=f[n]; If[s<51&&t[[s]]==0, t[[s]]=n], {n, 1, 4000}]; t
%o A081375 (PARI) lista(len) = {my(v = vector(len), c = 0, k = 1, i); while(c < len, i = #select(x -> x <= k, invphi(eulerphi(k))); if(i <= len && v[i] == 0, c++; v[i] = k); k++); v;} \\ _Amiram Eldar_, Nov 08 2024, using _Max Alekseyev_'s invphi.gp
%Y A081375 Cf. A000010, A008479, A081373, A081374, A067004.
%K A081375 nonn
%O A081375 1,2
%A A081375 _Labos Elemer_, Mar 24 2003