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 A233326 #23 Jul 05 2023 16:24:42
%S A233326 1,15,113,799,5601,39215,274513,1921599,13451201,94158415,659108913,
%T A233326 4613762399,32296336801,226074357615,1582520503313,11077643523199,
%U A233326 77543504662401,542804532636815,3799631728457713,26597422099203999,186181954694428001
%N A233326 a(n) = (7^(n+1) - 4) / 3.
%C A233326 Sum of n-th row of triangle of powers of 7: 1; 7 1 7; 49 7 1 7 49; 343 49 7 1 7 49 343; ...
%H A233326 Vincenzo Librandi, <a href="/A233326/b233326.txt">Table of n, a(n) for n = 0..200</a>
%H A233326 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (8,-7).
%F A233326 G.f.: (1+7*x)/((1-x)*(1-7*x)).
%F A233326 a(n) = 8*a(n-1) - 7*a(n-2) for n>1, a(0)=1, a(1)=15.
%F A233326 a(n) = 7*a(n-1) + 8 for n>0, a(0)=1.
%e A233326 a(0) = 1;
%e A233326 a(1) = 7 + 1 + 7 = 15;
%e A233326 a(2) = 49 + 7 + 1 + 7 + 49 = 113;
%e A233326 a(3) = 343 + 49 + 7 + 1 + 7 + 49 + 343 = 799; etc.
%t A233326 Table[(7^(n + 1) - 4)/3, {n, 0, 40}] (* _Vincenzo Librandi_, Feb 25 2014 *)
%t A233326 LinearRecurrence[{8,-7},{1,15},30] (* _Harvey P. Dale_, Jul 05 2023 *)
%o A233326 (Magma) [(7^(n+1)-4)/3: n in [0..30]]; // _Vincenzo Librandi_, Feb 25 2014
%K A233326 nonn,easy
%O A233326 0,2
%A A233326 _Philippe Deléham_, Feb 23 2014