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 A380542 #30 Jul 07 2025 10:44:03
%S A380542 1,0,1,6,10,6,8,18,22,7,30,18,4,42,46,13,58,10,22,70,3,78,82,44,24,25,
%T A380542 34,106,54,56,126,130,68,138,37,50,78,162,166,43,178,90,190,8,49,198,
%U A380542 210,222,226,114,116,238,60,250,128,262,67,30,138,140
%N A380542 a(n) is the multiplicative order of -9 modulo prime(n); a(2) = 0 for completion.
%H A380542 Jianing Song, <a href="/A380542/b380542.txt">Table of n, a(n) for n = 1..10000</a>
%t A380542 A380542[n_] := If[n == 2, 0, MultiplicativeOrder[-9, Prime[n]]];
%t A380542 Array[A380542, 100] (* _Paolo Xausa_, Jun 29 2025 *)
%o A380542 (PARI) a(n,{k=-9}) = my(p = prime(n)); if(k%p==0, 0, znorder(Mod(k,p)))
%Y A380542 Cf. A105881 (primes having primitive root -9).
%Y A380542 Cf. bases 2..10: A014664, A062117, A082654, A211241, A211242, A211243, A211244, A211245, A002371.
%Y A380542 Cf. bases -2..-10: A337878 (if first term 1), A380482, A380531, A380532, A380533, A380540, A380541, this sequence, A385222.
%K A380542 nonn,easy
%O A380542 1,4
%A A380542 _Jianing Song_, Jun 27 2025