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 A383720 #22 Jul 03 2025 10:57:28
%S A383720 3,5,35,197,1155,6725,39203,228485,1331715,7761797,45239075,263672645,
%T A383720 1536796803,8957108165,52205852195,304278004997,1773462177795,
%U A383720 10336495061765,60245508192803,351136554095045,2046573816377475,11928306344169797,69523264248641315
%N A383720 a(0)=3, a(1)=5, a(2)=35; a(n) = 5*a(n-1) + 5*a(n-2) - a(n-3) for n > 2.
%H A383720 Paolo Xausa, <a href="/A383720/b383720.txt">Table of n, a(n) for n = 0..1000</a>
%H A383720 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (5,5,-1).
%F A383720 G.f.: (3 - 10*x - 5*x^2)/((1 + x) * (1 - 6*x + x^2)).
%F A383720 a(n) = Pell(3*n)/Pell(n) for n > 0.
%t A383720 LinearRecurrence[{5, 5, -1}, {3, 5, 35}, 25] (* _Paolo Xausa_, Jul 03 2025 *)
%o A383720 (PARI) my(N=30, x='x+O('x^N)); Vec((3-10*x-5*x^2)/((1+x)*(1-6*x+x^2)))
%Y A383720 Cf. A000129, A002203, A047946, A084158.
%K A383720 nonn,easy
%O A383720 0,1
%A A383720 _Seiichi Manyama_, May 07 2025