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 A190973 #28 Sep 08 2022 08:45:57
%S A190973 0,1,7,45,287,1829,11655,74269,473263,3015765,19217303,122458061,
%T A190973 780337215,4972528261,31686348967,201914329725,1286654912207,
%U A190973 8198927066549,52245869817015,332925380452909,2121494183902303,13518757765504485,86145327622922183
%N A190973 a(n) = 7*a(n-1) - 4*a(n-2), with a(0) = 0, a(1) = 1.
%H A190973 G. C. Greubel, <a href="/A190973/b190973.txt">Table of n, a(n) for n = 0..1000</a>
%H A190973 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (7,-4).
%F A190973 a(n) = ((7/2 + 1/2*sqrt(33))^n - (7/2 - 1/2*sqrt(33))^n)/sqrt(33). - _Giorgio Balzarotti_, May 28 2011
%F A190973 G.f.: x/(1 - 7*x + 4*x^2). - _Philippe Deléham_, Oct 12 2011
%p A190973 seq( simplify(2^(n-1)*ChebyshevU(n-1, 7/4)), n=0..30); # _G. C. Greubel_, Dec 24 2019
%t A190973 LinearRecurrence[{7, -4}, {0, 1}, 30]
%t A190973 Table[2^(n - 1) * ChebyshevU[n - 1, 7/4], {n, 0, 30}] (* _G. C. Greubel_, Dec 24 2019 *)
%o A190973 (PARI) vector(31, n, 2^(n-2)*polchebyshev(n-2, 2, 7/4) ) \\ _G. C. Greubel_, Dec 24 2019
%o A190973 (Magma) I:=[0,1]; [n le 2 select I[n] else 7*Self(n-1) - 4*Self(n-2): n in [1..20]]; // _G. C. Greubel_, Dec 24 2019
%o A190973 (Sage) [2^(n-1)*chebyshev_U(n-1,7/4) for n in (0..30)] # _G. C. Greubel_, Dec 24 2019
%o A190973 (GAP) a:=[0,1];; for n in [3..30] do a[n]:=7*a[n-1]-4*a[n-2]; od; a; # _G. C. Greubel_, Dec 24 2019
%Y A190973 Cf. A190958 (index to generalized Fibonacci sequences).
%K A190973 nonn
%O A190973 0,3
%A A190973 _Vladimir Joseph Stephan Orlovsky_, May 24 2011