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 A385225 #18 Jun 28 2025 15:33:33 %S A385225 2,3,7,23,29,43,47,61,67,83,103,107,127,163,167,223,227,229,263,283, %T A385225 307,347,349,367,383,421,443,449,463,467,487,503,509,521,523,547,563, %U A385225 587,607,643,647,661,683,701,709,727,743,761,787,821,823,827,863,883,887,907,947,967,983 %N A385225 Primes p such that multiplicative order of -5 modulo p is odd. %C A385225 The multiplicative order of -5 modulo a(n) is A385231(n). %C A385225 Contained in primes congruent to 1, 3, 7, 9 modulo 20 (primes p such that -5 is a quadratic residue modulo p, A139513), and contains primes congruent to 3, 7 modulo 20 (A122870). %C A385225 Conjecture: this sequence has density 1/3 among the primes. %H A385225 Jianing Song, <a href="/A385225/b385225.txt">Table of n, a(n) for n = 1..10000</a> %t A385225 Select[Prime[Range[200]], OddQ[MultiplicativeOrder[-5, #]] &] (* _Paolo Xausa_, Jun 28 2025 *) %o A385225 (PARI) isA385225(p) = isprime(p) && (p!=5) && znorder(Mod(-5,p))%2 %Y A385225 Subsequence of A139513. Contains A122870 as a subsequence. %Y A385225 Cf. A385231 (the actual multiplicative orders). %Y A385225 Cf. other bases: A014663 (base 2), A385220 (base 3), A385221 (base 4), A385192 (base 5), A163183 (base -2), A385223 (base -3), A385224 (base -4), this sequence (base -5). %K A385225 nonn,easy %O A385225 1,1 %A A385225 _Jianing Song_, Jun 22 2025