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 A128058 #7 Jan 30 2020 21:29:16
%S A128058 1,2,1,-4,-9,2,43,72,-53,-418,-549,860,4161,4006,-11619,-41104,-24989,
%T A128058 145046,399571,89796,-1723259,-3787914,829841,19739016,34642741,
%U A128058 -26909998,-219300587,-300591148,467328447,2369124842
%N A128058 Expansion of 1/((1-x)sqrt(1-2x+5x^2)).
%C A128058 Partial sums of A098331. Binomial transform of A128057. Hankel transform is A128056.
%F A128058 a(n)=sum{k=0..n, sum{j=0..k, C(k,j)*C(k-j,j)*(-1)^j}}
%F A128058 D-finite with recurrence: n*a(n) +(-3*n+1)*a(n-1) +(7*n-6)*a(n-2) +5*(-n+1)*a(n-3)=0. - _R. J. Mathar_, Jan 23 2020
%t A128058 CoefficientList[Series[1/((1-x)Sqrt[1-2x+5x^2]),{x,0,50}],x] (* _Harvey P. Dale_, Jun 23 2018 *)
%K A128058 easy,sign
%O A128058 0,2
%A A128058 _Paul Barry_, Feb 13 2007