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 A123988 #24 Sep 08 2022 08:45:28 %S A123988 3,7,17,31,41,43,73,79,89,103,109,113,127,137,151,157,199,223,229,233, %T A123988 241,251,257,271,277,281,283,331,337,353,367,397,401,433,439,449,457, %U A123988 463,487,521,569,571,593,601,607,617,631,641,673,683,691,727,733,739,751,761,809,811,823,857,881,911 %N A123988 Primes p such that 2^x == 3 (mod p) has no solutions. %C A123988 Such primes cannot divide solutions to 2^m == 3 (mod m) (see A050259). %H A123988 J. K. Crump, <a href="https://web.archive.org/web/20120104074339/http://www.immortaltheory.com:80/NumberTheory/">Number Theory Web</a>. %o A123988 (Magma) lst:=[3]; for p in [5..911 by 2] do if IsPrime(p) then t:=0; e:=Ceiling(Log(2, p+1)); for x in [e..p-2] do if 2^x mod p eq 3 then t:=1; break; end if; end for; if t eq 0 then Append(~lst, p); end if; end if; end for; lst; // _Arkadiusz Wesolowski_, Jan 12 2021 %Y A123988 Cf. A050259, A001915 (complement in the primes). %K A123988 nonn %O A123988 1,1 %A A123988 _Artur Jasinski_, Nov 23 2006 %E A123988 Edited by _Max Alekseyev_, Jan 14 2007 %E A123988 Corrected by _Max Alekseyev_, Jun 08 2011 %E A123988 Corrected by _Arkadiusz Wesolowski_, Jan 12 2021