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 A067230 #14 Aug 22 2015 17:20:44 %S A067230 1,3,5,10,11,23,33,46,65,77,123,136,221,371,383,423,483,513,545,670, %T A067230 753,1643,2033,3838,3885,4533,4798,5177,7463,7739,8201,8985,9010,9393, %U A067230 12256,13144,14104,17110,17147,17663,18695,19817,21119,23038,24695 %N A067230 Numbers n such that phi(2n-1) = sigma(n). %H A067230 Donovan Johnson, <a href="/A067230/b067230.txt">Table of n, a(n) for n = 1..1000</a> %t A067230 Select[Range[25000],EulerPhi[2#-1]==DivisorSigma[1,#]&] (* _Harvey P. Dale_, Aug 22 2015 *) %o A067230 (PARI) isok(n) = eulerphi(2*n-1) == sigma(n); \\ _Michel Marcus_, Nov 21 2013 %Y A067230 Cf. A000010, A000203, A067229. %K A067230 nonn %O A067230 1,2 %A A067230 _Benoit Cloitre_, Feb 20 2002