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 A066902 #22 Apr 06 2020 11:37:50 %S A066902 3,5,20,156,254,377,593,1800,5903,5981,7925,18669,19240,41274,48296, %T A066902 135700,146866,228028,234303,251216,407377,654288,802222,886223, %U A066902 938654,1063412,1072766,1212140,1238668,1515063,1609346,2080991,2097725,2363130,2408674,2916514 %N A066902 Integers k such that phi(prime(k)+1) = phi(prime(k)-1). %C A066902 Integers k such that A008331(k) = A008330(k). %H A066902 Giovanni Resta, <a href="/A066902/b066902.txt">Table of n, a(n) for n = 1..675</a> %F A066902 a(n) = primepi(A067890(n)). - _Giovanni Resta_, Apr 06 2020 %t A066902 Select[Range[1000000],EulerPhi[Prime[#]-1]==EulerPhi[Prime[#]+1]&] (* _Harvey P. Dale_, Feb 25 2012 *) %o A066902 (PARI) isok(k) = my(p=prime(k)); eulerphi(p+1) == eulerphi(p-1); \\ _Michel Marcus_, Apr 06 2020 %Y A066902 Cf. A000010, A008864, A006093, A008330, A008331, A067890. %K A066902 nonn %O A066902 1,1 %A A066902 _Benoit Cloitre_, Jan 26 2002 %E A066902 More terms from _Harvey P. Dale_, Feb 25 2012 %E A066902 More terms from _Jinyuan Wang_, Apr 05 2020