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 A213049 #12 Sep 08 2022 08:46:02
%S A213049 5,37,73,101,109,197,257,577,601,641,677,727,1601,1801,2593,3137,3389,
%T A213049 3457,4057,4357,5477,8101,8837,10369,14401,14407,16901,17957,18253,
%U A213049 18433,20809,21317,22501,25601,30977,33857,37447,42437,44101,47629,47653,50177
%N A213049 Primes p such that the order of 2 mod p is a square.
%H A213049 Vincenzo Librandi, <a href="/A213049/b213049.txt">Table of n, a(n) for n = 1..178</a>
%e A213049 The order of 2 mod 601 is 25, which is a square, so 601 is a term.
%o A213049 (PARI)
%o A213049 { forprime (p=3, 10^6,
%o A213049 r = znorder(Mod(2,p));
%o A213049 if ( issquare(r), print1(p,", ") );
%o A213049 ); }
%o A213049 (Magma) [NthPrime(n): n in [2..6275] | IsSquare(Modorder(2, NthPrime(n)))]; // _Bruno Berselli_, Jun 08 2012
%Y A213049 Cf. A014662, A014663, A122094.
%K A213049 nonn
%O A213049 1,1
%A A213049 _Joerg Arndt_, Jun 03 2012