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 A067890 #18 Sep 16 2022 12:40:28 %S A067890 5,11,71,911,1609,2591,4339,15401,58309,59149,80989,208391,215389, %T A067890 496511,589189,1809079,1970149,3167569,3260809,3516109,5914369, %U A067890 9832271,12231311,13608071,14470061,16537151,16692551,19018369,19462661 %N A067890 Primes p such that phi(p+1) = phi(p-1). %C A067890 Primes in A066812. %H A067890 Giovanni Resta, <a href="/A067890/b067890.txt">Table of n, a(n) for n = 1..675</a> %F A067890 a(n) = prime(A066902(n)). - _Giovanni Resta_, Apr 06 2020 %t A067890 Select[Prime[Range[124*10^4]],EulerPhi[#-1]==EulerPhi[#+1]&] (* _Harvey P. Dale_, Apr 09 2019 *) %o A067890 (PARI) v=[]; forprime(p=2,40000000,if(eulerphi(p+1)==eulerphi(p-1),v=concat(v,p))); v %Y A067890 Cf. A066902, A066812. %K A067890 easy,nonn %O A067890 1,1 %A A067890 _Benoit Cloitre_, Mar 02 2002 %E A067890 More terms from _Rick L. Shepherd_, May 03 2002