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 A067933 #21 Apr 18 2025 09:57:25
%S A067933 2,3,5,7,11,31,71,2591,131071
%N A067933 Primes p such that p == -1 (mod phi(p-1)).
%C A067933 No more terms up to 373587883 (the 20 millionth prime).
%t A067933 Do[p = Prime[n]; If[ Mod[p + 1, EulerPhi[p - 1]] == 0, Print[p]], {n, 1, 10^8}] (* Cloitre *)
%t A067933 Select[Prime[Range[10^5]], Mod[#, EulerPhi[# - 1]] == EulerPhi[# - 1] - 1 &] (* _Alonso del Arte_, Sep 26 2011 *)
%o A067933 (PARI) list(lim) = forprime(p = 1, lim, if(!((p+1) % eulerphi(p-1)), print1(p,", "))); \\ _Amiram Eldar_, Apr 18 2025
%Y A067933 Cf. A000010, A008330.
%K A067933 nonn,more
%O A067933 1,1
%A A067933 _Benoit Cloitre_, Feb 22 2002
%E A067933 Edited by _Robert G. Wilson v_, Feb 27 2002