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 A122918 #31 Jan 12 2016 10:58:05
%S A122918 1,0,-2,2,1,-4,3,2,-6,4,3,-8,5,4,-10,6,5,-12,7,6,-14,8,7,-16,9,8,-18,
%T A122918 10,9,-20,11,10,-22,12,11,-24,13,12,-26,14,13,-28,15,14,-30,16,15,-32,
%U A122918 17,16,-34,18,17,-36,19,18,-38
%N A122918 Expansion of (1+x)^2/(1+x+x^2)^2.
%C A122918 Row sums of Riordan array (1/(1+x+x^2), x/(1+x)^2), A122917.
%C A122918 For n>=1, a(n) equals (-1)^(n+1) times the second immanant of the n X n matrix with 1's along the main diagonal, superdiagonal, and subdiagonal, and 0's everywhere else. The second immanant of an n X n matrix A is the immanant of A given by the partition (2, 1^(n-2)). - _John M. Campbell_, Apr 12 2014
%H A122918 Vincenzo Librandi, <a href="/A122918/b122918.txt">Table of n, a(n) for n = 0..1000</a>
%H A122918 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (-2,-3,-2,-1).
%F A122918 a(n) = 4 * sqrt(3) * cos(2*Pi*n/3 + Pi/6)/9 + 2(n+1) * sin(2*Pi*n/3 + Pi/6)/3. a(n) = sum{k=0..n} A057078(k) * A057078(n-k).
%F A122918 a(n) = (-1)^(n+1)*sum((-1)^i*binomial(n-i,i)*(n-2*i-1), i=0..[n/2]). - _John M. Campbell_, Jan 08 2016
%t A122918 CoefficientList[Series[(1 + x)^2/(1 + x + x^2)^2, {x, 0, 100}], x] (* _Vincenzo Librandi_, Apr 13 2014 *)
%t A122918 Print[Table[(-1)^(n+1)*Sum[Binomial[n-i, i]*(n-2*i-1)*(-1)^i, {i, 0, Floor[n/2]}], {n, 0, 100}]] ; (* _John M. Campbell_, Jan 08 2016 *)
%o A122918 (PARI) Vec((1+x)^2/(1+x+x^2)^2 + O(x^100)) \\ _Altug Alkan_, Jan 08 2015
%o A122918 (PARI) A122918(n)=(-1)^(n+1)*sum(i=0,n\2,(-1)^i*binomial(n-i,i)*(n-2*i-1)) \\ _M. F. Hasler_, Jan 12 2016
%Y A122918 Cf. A187430 (series reversion, with offset 1).
%K A122918 easy,sign
%O A122918 0,3
%A A122918 _Paul Barry_, Sep 19 2006