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 A067261 #17 May 29 2018 03:06:29 %S A067261 1,4,5,9,10,21,32,34,45,55,65,68,70,129,153,160,176,183,203,245,340, %T A067261 370,407,441,550,580,635,741,765,806,845,965,1011,1025,1089,1166,1247, %U A067261 1292,1505,1508,1840,2271,2402,2584,2590,3285,3604,4065,4223,4832,5339 %N A067261 Numbers n such that sigma(n+1)=3*phi(n). %H A067261 Robert Israel, <a href="/A067261/b067261.txt">Table of n, a(n) for n = 1..1000</a> %p A067261 select(n -> numtheory:-sigma(n+1)=3*numtheory:-phi(n), [$1..10000]); # _Robert Israel_, May 29 2018 %t A067261 Select[Range[6000],DivisorSigma[1,#+1]==3*EulerPhi[#]&] (* _Harvey P. Dale_, Jun 11 2017 *) %o A067261 (PARI) isok(n) = sigma(n+1) == 3*eulerphi(n); \\ _Michel Marcus_, May 29 2018 %Y A067261 Cf. A000010, A000203. %K A067261 nonn %O A067261 1,2 %A A067261 _Benoit Cloitre_, Feb 21 2002