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 A190960 #39 Jan 05 2025 09:40:12
%S A190960 0,1,3,3,-9,-45,-81,27,567,1539,1215,-5589,-24057,-38637,28431,317115,
%T A190960 780759,439587,-3365793,-12734901,-18009945,22379571,175198383,
%U A190960 391317723,122762871,-1979617725,-6675430401,-8148584853,15606827847,95711992659,193495010895
%N A190960 a(n) = 3*a(n-1) - 6*a(n-2), with a(0)=0, a(1)=1.
%H A190960 G. C. Greubel, <a href="/A190960/b190960.txt">Table of n, a(n) for n = 0..1000</a>
%H A190960 Taras Goy and Mark Shattuck, <a href="https://doi.org/10.2478/amsil-2023-0027">Determinants of Toeplitz-Hessenberg Matrices with Generalized Leonardo Number Entries</a>, Ann. Math. Silesianae (2023). See p. 16.
%H A190960 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,-6).
%F A190960 G.f.: x/(1-3*x+6*x^2). - _Philippe Deléham_, Oct 11 2011
%F A190960 a(n) = (i/sqrt(15))*((3/2 - i*sqrt(15)/2)^n - (3/2 + i*sqrt(15)/2)^n), where i=sqrt(-1). - _Taras Goy_, Jan 04 2025
%F A190960 E.g.f.: 2*exp(3*x/2)*sin(sqrt(15)*x/2)/sqrt(15). - _Stefano Spezia_, Jan 05 2025
%t A190960 LinearRecurrence[{3,-6}, {0,1}, 50]
%o A190960 (PARI) x='x+O('x^30); concat([0], Vec(x/(1-3*x+6*x^2))) \\ _G. C. Greubel_, Jan 25 2018
%o A190960 (Magma) I:=[0,1]; [n le 2 select I[n] else 3*Self(n-1) - 6*Self(n-2): n in [1..30]]; // _G. C. Greubel_, Jan 25 2018
%Y A190960 Cf. A190958 (index to generalized Fibonacci sequences).
%K A190960 sign,easy
%O A190960 0,3
%A A190960 _Vladimir Joseph Stephan Orlovsky_, May 24 2011