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 A067229 #16 Sep 06 2024 17:25:31 %S A067229 6,7,27,38,55,85,87,127,188,236,255,266,445,451,655,717,913,1309,1357, %T A067229 1490,1947,2095,2515,2726,3002,3247,3289,4117,4237,5071,5605,7195, %U A067229 8924,12128,12625,12771,12837,13190,13795,15835,16197,16748,17997,20257 %N A067229 Numbers n such that phi(2n+1) = sigma(n). %H A067229 Donovan Johnson, <a href="/A067229/b067229.txt">Table of n, a(n) for n = 1..1000</a> %t A067229 Select[Range[21000],EulerPhi[2#+1]==DivisorSigma[1,#]&] (* _Harvey P. Dale_, Sep 06 2024 *) %o A067229 (PARI) isok(n) = eulerphi(2*n+1) == sigma(n); \\ _Michel Marcus_, Nov 21 2013 %Y A067229 Cf. A000010, A000203, A037225, A067230. %K A067229 nonn %O A067229 1,1 %A A067229 _Benoit Cloitre_, Feb 20 2002