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 A161785 #10 Feb 18 2021 01:34:29
%S A161785 1,4,6,8,12,18,20,24,28,30,32,36,40,42,44,48,54,56,60,72,78,80,84,96,
%T A161785 102,104,108,110,112,120,126,128,132,138,140,144,150,156,160,162,164,
%U A161785 168,176,180,192,198,200,204,210,212,216,222,224,228,240,252,256,260
%N A161785 Numbers k that are in the range of both Euler's phi function and the sigma function.
%C A161785 That is, for each k there exist x and y such that k = phi(x) = sigma(y). Sigma is the sum of divisors function. Ford, Luca, and Pomerance prove that this sequence is infinite.
%D A161785 R. K. Guy, Unsolved Problems in Number Theory, B38.
%H A161785 T. D. Noe, <a href="/A161785/b161785.txt">Table of n, a(n) for n = 1..10000</a>
%H A161785 Kevin Ford, Florian Luca, and Carl Pomerance, <a href="http://arxiv.org/abs/0906.3380">Common values of the arithmetic functions phi and sigma</a>, Bull. London Math. Soc. 42 (2010), pp. 478-488.
%F A161785 Intersection of A002202 and A002191.
%t A161785 Intersection[EulerPhi[Range[9660]], DivisorSigma[1,Range[2112]]]
%o A161785 (PARI) list(lim)={
%o A161785 my(u=vector(lim\=1,k,sigma(k)),v=vector(if(lim>63,3*lim*log(log(lim))\1,210),k,eulerphi(k)));
%o A161785 select(n->n<=lim,setintersect(vecsort(v,,8),vecsort(u,,8)))
%o A161785 }; \\ _Charles R Greathouse IV_, Feb 05 2013
%K A161785 nonn
%O A161785 1,2
%A A161785 _T. D. Noe_, Jun 19 2009