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 A073815 #21 Dec 18 2024 21:59:57
%S A073815 1,3,18,12,200,14,3364,15,722,328,9801,42,25281,116,1800,165,36992,
%T A073815 810,4414201,88,196,29161,541696,35,2928200,1413,103968,172,98942809,
%U A073815 488,1547536,336,19602,17536,814088,370,49042009,55297,1521,319,3150464641
%N A073815 Least number x such that gcd(phi(x), sigma(x)) = n.
%C A073815 Values are frequently identical to terms of A077102. Since gcd(a,b) and gcd(a+b,a-b) may differ, so may the smallest solutions. A077102(m) and a(m) differ at m = 1, 2, 4, 8, 16, 28, 32, 40, etc.
%H A073815 Giovanni Resta, <a href="/A073815/b073815.txt">Table of n, a(n) for n = 1..120</a>
%F A073815 a(n) = Min{x; A055008(x)=n}. a(n)=Min{x; gcd(A000203(x), A000010(x))=n}
%F A073815 a(n) = Min{x: A023897(x)= n}, smallest balanced number (A020492) for which the quotient equals n.
%t A073815 f[x_] := Apply[GCD, {DivisorSigma[1, x], EulerPhi[x]}] t=Table[0, {100}]; Do[s=f[n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 10^13}];
%o A073815 (PARI) a(n)=my(x=n);while(gcd(eulerphi(x),sigma(x))!=n, x++); x \\ _Charles R Greathouse IV_, Dec 09 2013
%Y A073815 Cf. A000203, A000010, A009223, A055008, A077099-A077102, A051612, A065387, A023897, A020492.
%K A073815 nonn
%O A073815 1,2
%A A073815 _Labos Elemer_, Nov 12 2002