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 A123008 #19 Sep 08 2022 08:45:28
%S A123008 1,5,35,195,1265,7405,46435,277995,1716865,10383605,63688835,
%T A123008 386967795,2366156465,14406507805,87966927235,536096549595,
%U A123008 3271366280065,19945146300005,121674449601635,741977556703395,4525816353447665
%N A123008 Expansion of x*(1 + 3*x)/(1 - 2*x - 25*x^2).
%H A123008 G. C. Greubel, <a href="/A123008/b123008.txt">Table of n, a(n) for n = 1..1000</a>
%H A123008 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,25).
%F A123008 From _Colin Barker_, Oct 19 2012: (Start)
%F A123008 a(n) = 2*a(n-1) + 25*a(n-2) for n>2.
%F A123008 G.f.: x*(1+3*x)/(1-2*x-25*x^2). (End)
%F A123008 a(n) = (5*i)^(n-2)*(3*ChebyshevU(n-2, -i/5) + 5*i*ChebyshevU(n-1, -i/5)). - _G. C. Greubel_, Jul 13 2021
%t A123008 M:= {{0, 5}, {5, 2}}; v[1] = {1, 1}; v[n_]:= v[n]= M.v[n-1];
%t A123008 Table[v[n][[1]], {n, 30}]
%o A123008 (Magma) [n le 2 select 5^(n-1) else 2*Self(n-1) + 25*Self(n-2): n in [1..31]]; // _G. C. Greubel_, Jul 13 2021
%o A123008 (Sage) [(5*i)^(n-2)*(3*chebyshev_U(n-2, -i/5) + 5*i*chebyshev_U(n-1, -i/5)) for n in (1..30)] # _G. C. Greubel_, Jul 13 2021
%Y A123008 Cf. A002534, A123004.
%K A123008 nonn,easy
%O A123008 1,2
%A A123008 _Roger L. Bagula_ and _Gary W. Adamson_, Sep 23 2006
%E A123008 Sequence edited by _Joerg Arndt_ and _Colin Barker_, Oct 19 2012