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 A074390 #15 Nov 14 2024 06:01:17
%S A074390 1,6,18,12,200,42,196,56,459,950,5203,396,9243,980,1800,336,19363,270,
%T A074390 13357,600,1764,10406,72473,168,18625,34814,4293,812,145493,1350,
%U A074390 15376,992,19602,38726,41615,1836,99937,26714,1521,440,274003,3822,475193
%N A074390 a(n) is the least number k that A074389(k) = n.
%H A074390 Amiram Eldar, <a href="/A074390/b074390.txt">Table of n, a(n) for n = 1..1000</a>
%F A074390 a(n) = Min{x; GCD(x, sigma(x), phi(x)) = n} = Min{x; GCD(x, A000005(x), A000010(x)) = n}.
%e A074390 For n = 79: a(79) = 979837 because GCD(979837,998718,961272) = 79 and 979837 is the smallest.
%t A074390 f[x_] := GCD[DivisorSigma[1, x], EulerPhi[x], x]; t=Table[0, {100}]; Do[s=f[n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 1000000}]; t
%o A074390 (PARI) lista(len) = {my(v = vector(len), c = 0, k = 1, f, i); while(c < len, f = factor(k); i = gcd([k, sigma(k), eulerphi(k)]); if(i <= len && v[i] == 0, c++; v[i] = k); k++); v;} \\ _Amiram Eldar_, Nov 14 2024
%Y A074390 Cf. A000005, A000010, A073815, A050399, A009195, A009194.
%K A074390 nonn
%O A074390 1,2
%A A074390 _Labos Elemer_, Aug 23 2002