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 A106192 #13 Oct 01 2021 18:14:30
%S A106192 1,-2,-1,-6,-11,-34,-95,-298,-953,-3158,-10677,-36750,-128249,-452774,
%T A106192 -1614049,-5801654,-21003739,-76516994,-280293319,-1031794394,
%U A106192 -3814819699,-14160035234,-52747353739,-197125162514,-738866581039,-2776933457162,-10462759383943
%N A106192 Expansion of sqrt(1-4x)/(1-x^2).
%C A106192 Diagonal sums of number triangle A106190.
%F A106192 a(n) = Sum_{k=0..floor(n/2)} binomial(2*(n-2*k), n-2*k)/(1-2*(n-2*k)).
%F A106192 D-finite with recurrence: n*a(n) +2*(-2*n+3)*a(n-1) -n*a(n-2) +2*(2*n-3)*a(n-3)=0. - _R. J. Mathar_, Nov 28 2014
%t A106192 CoefficientList[Series[Sqrt[1-4x]/(1-x^2),{x,0,30}],x] (* _Harvey P. Dale_, Apr 24 2012 *)
%Y A106192 Cf. A106190.
%K A106192 easy,sign
%O A106192 0,2
%A A106192 _Paul Barry_, Apr 24 2005