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 A139686 #12 Jun 27 2025 10:54:36 %S A139686 3,11,5,23,35,9,39,11,51,7,15,83,95,99,37,29,119,131,135,155,21,179, %T A139686 183,191,43,73,231,239,243,251,299,25,303,45,323,359,121,371,375,411, %U A139686 419,431,55,443,91,153,117,483,491,495,515,519,531,543,29,575,611,615,639 %N A139686 Odd multiplicative orders of 2 modulo primes. %C A139686 Subsequence of A014664, consisting of odd elements. %H A139686 Amiram Eldar, <a href="/A139686/b139686.txt">Table of n, a(n) for n = 1..10000</a> %F A139686 a(n) = multiplicative order of 2 modulo A014663(n). %t A139686 p = Select[Range[1000], PrimeQ]; Select[MultiplicativeOrder[2, #] & /@ p, OddQ] (* _Amiram Eldar_, Jul 30 2020 *) %o A139686 (PARI) forprime(p=3,10^5,z=znorder(Mod(2,p));if(z%2,print1(z,", "))) %Y A139686 Cf. A014664, A014663 (corresponding primes). %Y A139686 Cf. other bases: this sequence (base 2), A385226 (base 3), A385227 (base 4), A385193 (base 5), A385228 (base -2), A385229 (base -3), A385230 (base -4), A385231 (base -5). %K A139686 nonn %O A139686 1,1 %A A139686 _Max Alekseyev_, Apr 29 2008