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 A119388 #4 Jan 21 2019 19:01:55 %S A119388 2,3,5,7,11,31,71,511,2591,131071,3359231,167247871,8589934591 %N A119388 Numbers n such that n == -1 (mod phi(n-1)). %C A119388 This sequence has the terms from A067933 (all primes), plus 511 and 3359231 that are not primes. %C A119388 Checked up to x<70000000 %C A119388 a(14) > 10^11. [From _Donovan Johnson_, Aug 08 2010] %o A119388 (PARI) for(x=1,70000000,if(((x)+1)%eulerphi((x)-1)==0,print((x)))) %Y A119388 Cf. A067933. %K A119388 nonn %O A119388 1,1 %A A119388 _Jorge Coveiro_, Jul 25 2006 %E A119388 a(13) from _Donovan Johnson_, Aug 08 2010