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 A077876 #30 Aug 22 2024 09:17:32
%S A077876 1,2,1,-2,-3,2,9,6,-11,-22,1,46,45,-46,-135,-42,229,314,-143,-770,
%T A077876 -483,1058,2025,-90,-4139,-3958,4321,12238,3597,-20878,-28071,13686,
%U A077876 69829,42458,-97199,-182114,12285,376514,351945,-401082,-1104971,-302806,1907137,2512750,-1301523,-6327022
%N A077876 Expansion of (1-x)^(-1)/(1-x+2*x^2).
%C A077876 Row sums of Riordan array (1/(1-x),x(1-2x)). - _Paul Barry_, Jul 18 2005
%H A077876 <a href="/index/Ch#Cheby">Index entries for sequences related to Chebyshev polynomials.</a>
%H A077876 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,-3,2).
%F A077876 a(n) = Sum_{k=0..n} U(k, 1/(2*sqrt(2)))*sqrt(2)^k. - _Paul Barry_, Nov 20 2003 [There is a missing parenthesis, but it is not clear where it should be inserted. - _N. J. A. Sloane_, Feb 08 2015] [corrected by _Jason Yuen_, Aug 22 2024]
%F A077876 a(n) = Sum_{k=2..n-2} A107920(k). - _R. J. Mathar_, Oct 13 2017
%F A077876 a(n) = Sum_{k=0..floor((n+1)/2)} binomial(n+1-k,k+1)*(-2)^k, n>=0. - _Taras Goy_, Apr 15 2020
%t A077876 Join[{a=1,b=2},Table[c=b-2*a+1;a=b;b=c,{n,100}]] (* _Vladimir Joseph Stephan Orlovsky_, Jan 21 2011 *)
%o A077876 (PARI) Vec(1/((1-x)*(1-x+2*x^2)) + O(x^75)) \\ _Michel Marcus_, Feb 08 2015
%Y A077876 Cf. A001045, A107920.
%K A077876 sign,easy
%O A077876 0,2
%A A077876 _N. J. A. Sloane_, Nov 17 2002