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 A225585 #18 Sep 08 2022 08:46:05
%S A225585 2,4,8,20,48,121,312,820,2186,5904,16104,44286,122640,341640,956593,
%T A225585 2690420,7596480,21523360,61171656,174339220,498112057,1426411800,
%U A225585 4093181688,11767897353,33891544377,97764070320,282429536480,817028301962,2366564736720
%N A225585 Floor((3^n-1)/n).
%H A225585 Vincenzo Librandi, <a href="/A225585/b225585.txt">Table of n, a(n) for n = 1..300</a>
%t A225585 Table[Floor[(3^n - 1) / n], {n, 30}] (* or *) Table[Quotient[3^n - 1, n], {n, 30}]
%o A225585 (Magma) [Floor((3^n-1)/n): n in [1..30]];
%Y A225585 Cf. A003462, A007051, A024023, A034472, A082482, A092763.
%K A225585 nonn,easy
%O A225585 1,1
%A A225585 _Vincenzo Librandi_, May 30 2013