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 A106805 #28 Sep 02 2024 04:30:56
%S A106805 1,2,5,11,25,56,126,283,636,1429,3211,7215,16212,36428,81853,183922,
%T A106805 413269,928607,2086561,4688460,10534874,23671647,53189708,119516189,
%U A106805 268550439,603427359,1355888968,3046654856,6845771321,15382308530,34563733525,77664004259
%N A106805 Expansion of g.f.: 1/(1 - 2*x - x^2 + x^3).
%C A106805 Essentially the same as A006054. - _Joerg Arndt_, Nov 08 2022
%H A106805 G. C. Greubel, <a href="/A106805/b106805.txt">Table of n, a(n) for n = 0..1000</a>
%H A106805 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,-1).
%F A106805 G.f. for sequence with 1 prepended: 1/( 1 - Sum_{k>=0} x*(x+x^2-x^3)^k ). - _Joerg Arndt_, Sep 30 2012
%t A106805 LinearRecurrence[{2,1,-1}, {1,2,5}, 35] (* _Vladimir Joseph Stephan Orlovsky_, Feb 13 2012 *)
%o A106805 (PARI) Vec( 1/(1-2*x-x^2+x^3) + O(x^66) ) /* _Joerg Arndt_, Sep 30 2012 */
%o A106805 (Magma) I:=[1,2,5]; [n le 3 select I[n] else 2*Self(n-1) +Self(n-2) -Self(n-3): n in [1..36]]; // _G. C. Greubel_, Sep 11 2021
%o A106805 (Sage)
%o A106805 def A106805_list(prec):
%o A106805 P.<x> = PowerSeriesRing(ZZ, prec)
%o A106805 return P( 1/(1-2*x-x^2+x^3) ).list()
%o A106805 A106805_list(35) # _G. C. Greubel_, Sep 11 2021
%Y A106805 A006054 shifted left twice.
%K A106805 nonn,easy
%O A106805 0,2
%A A106805 _Roger L. Bagula_, May 17 2005
%E A106805 Edited by the Associate Editors of the OEIS, Apr 09 2009
%E A106805 Name corrected by _Joerg Arndt_, Sep 30 2012