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 A343575 #24 Jun 07 2021 10:25:22
%S A343575 0,9,0,49,0,9,0,129,60,49,0,49,0,9,100,129,0,249,0,49,340,9,0,449,0,9,
%T A343575 240,289,0,249,0,129,60,9,600,49,0,9,580,449,0,609,0,289,700,9,0,449,
%U A343575 700,249,60,289,0,969,200,129,60,9,0,49,0,9,1240,769,0,369,0
%N A343575 a(n) = floor((2+sqrt(5))^n - 2^(n+1)) mod (20*n).
%C A343575 Whenever n is an odd prime, a(n) is 0 (see M. Penn).
%H A343575 Jianing Song, <a href="/A343575/b343575.txt">Table of n, a(n) for n = 1..10000</a>
%H A343575 M. Penn, <a href="https://www.youtube.com/watch?v=hUh_j-uZdXI">Hello, old friend...</a>, YouTube video.
%F A343575 From _Jianing Song_, Jun 07 2021: (Start)
%F A343575 For even n, a(n) = 10*(A345031(n) mod (2*n)) - 1;
%F A343575 For odd n, a(n) = 10*(A345031(n) mod (2*n)). (End)
%t A343575 Table[Mod[Floor[(2+Sqrt[5])^n-2^(n+1)],20n],{n,67}] (* _Stefano Spezia_, Apr 21 2021 *)
%o A343575 (PARI) a(n) = my(M = [6, -7, -2; 1, 0, 0; 0, 1, 0]); 10*((M^n)[3, 1] % (2*n)) - !(n%2) \\ _Jianing Song_, Jun 07 2021
%Y A343575 Cf. A345031.
%K A343575 nonn,easy
%O A343575 1,2
%A A343575 _William C. Laursen_, Apr 20 2021
%E A343575 More terms from _Stefano Spezia_, Apr 21 2021