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 A239131 #16 Sep 08 2022 08:46:07
%S A239131 80,40,20,10,5,43,62,31,56,28,14,7,44,22,11,46,23,52,26,13,47,64,32,
%T A239131 16,8,4,2,1,41,61,71,76,38,19,50,25,53,67,74,37,59,70,35,58,29,55,68,
%U A239131 34,17,49,65,73,77,79,80,40,20,10,5,43,62,31,56,28,14,7,44
%N A239131 A sequence with period length 54; the companion of x(n) = A239130(n), the smallest positive solution of 3^4*x - 2^n*y = 1 for n >= 0.
%C A239131 The first 54 = phi(3^4) values of a(n) = y0(4, n) have been given, with phi(n) = A000010(n). They give a permutation of the smallest positive restricted residue class modulo 3^4.
%C A239131 The companion sequence is x0(4, n) = x(n) = A239130(n), n >= 0.
%C A239131 One could give a lengthy G.f.
%H A239131 Vincenzo Librandi, <a href="/A239131/b239131.txt">Table of n, a(n) for n = 0..1000</a>
%F A239131 a(n) = y0(4, n) == ((3^4 + 1)/2)^(n + 3^3) (mod 3^4), n >= 0.
%F A239131 a(n + 54) = a(n), n >= 0.
%e A239131 a(0) = 41^27 (mod 81) = 80.
%t A239131 Table[Mod[41^(n + 27), 81], {n, 0, 100}] (* _Vincenzo Librandi_, Mar 23 2014 *)
%t A239131 PowerMod[41,Range[0,100]+27,81] (* _Harvey P. Dale_, Dec 04 2018 *)
%o A239131 (Magma) [41^(n+27) mod 81: n in [0..80]]; // _Vincenzo Librandi_, Mar 23 2014
%Y A239131 Cf. A239130.
%K A239131 nonn,easy
%O A239131 0,1
%A A239131 _Wolfdieter Lang_, Mar 22 2014
%E A239131 More terms from _Vincenzo Librandi_, Mar 23 2014