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 A102303 #19 Feb 04 2024 03:22:30
%S A102303 1,9,57,401,2801,19609,137257,960801,6725601,47079209,329554457,
%T A102303 2306881201,16148168401,113037178809,791260251657,5538821761601,
%U A102303 38771752331201,271402266318409,1899815864228857,13298711049602001,93090977347214001,651636841430498009
%N A102303 a(n) = (1/6) * (7^(n+1) - 3*(-1)^n + 2).
%H A102303 G. C. Greubel, <a href="/A102303/b102303.txt">Table of n, a(n) for n = 0..1000</a>
%H A102303 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (7,1,-7).
%F A102303 From _Chai Wah Wu_, Mar 11 2021: (Start)
%F A102303 a(n) = 7*a(n-1) + a(n-2) - 7*a(n-3) for n > 2.
%F A102303 G.f.: -(1 + 2*x - 7*x^2)/((1 - x)*(1 + x)*(1 - 7*x)). (End)
%F A102303 From _G. C. Greubel_, Feb 03 2024: (Start)
%F A102303 a(n) = A023000(n+1) + A000035(n).
%F A102303 E.g.f.: (1/6)*(-3*exp(-x) + 2*exp(x) + 7*exp(7*x)). (End)
%t A102303 Table[(7^(n+1) -3*(-1)^n +2)/6, {n, 0, 50}]
%o A102303 (Magma) [(7^(n+1)-3*(-1)^n+2)/6: n in [0..50]]; // _G. C. Greubel_, Feb 03 2024
%o A102303 (SageMath) [(7^(n+1)-3*(-1)^n+2)/6 for n in range(51)] # _G. C. Greubel_, Feb 03 2024
%Y A102303 Cf. A000035, A023000.
%K A102303 nonn,easy
%O A102303 0,2
%A A102303 _Roger L. Bagula_, Mar 15 2005
%E A102303 Edited by _N. J. A. Sloane_, May 29 2007