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 A074891 #9 Feb 11 2014 19:05:30 %S A074891 15,35,357,1045,3339,5049,10659,12441,24871,24969,29029,50065,58435, %T A074891 64285,87685,99693,132957,137885,140335,353133,423657,596037,655707, %U A074891 734517,745503,894387,1390753,1406427,1529983,1641783,1739507,1823877 %N A074891 Numbers n such that sigma(n) = phi(3n). %H A074891 Donovan Johnson, <a href="/A074891/b074891.txt">Table of n, a(n) for n = 1..500</a> %e A074891 sigma(15) = 24 = phi(3 * 15), so 15 is a term of the sequence. %t A074891 Select[ Range[1936556], EulerPhi[3# ] == DivisorSigma[1, # ] &] %o A074891 (PARI) is(n)=sigma(n)==eulerphi(3*n) \\ _Charles R Greathouse IV_, Dec 09 2013 %K A074891 nonn %O A074891 1,1 %A A074891 _Joseph L. Pe_, Sep 13 2002 %E A074891 Edited and extended by _Robert G. Wilson v_, Sep 17 2002