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 A025577 #20 Jul 02 2018 06:35:37
%S A025577 1,3,7,17,43,113,305,839,2339,6585,18677,53283,152725,439455,1268623,
%T A025577 3672457,10656691,30988249,90275989,263425651,769801873,2252531971,
%U A025577 6599018227,19353381877,56814946381,166940119063,490930181515,1444813563869
%N A025577 Expansion of (x/(1-x))*sqrt((1+x)/(1-3*x)).
%H A025577 G. C. Greubel, <a href="/A025577/b025577.txt">Table of n, a(n) for n = 1..1000</a>
%F A025577 a(n) ~ 3^(n-1/2)/(sqrt(Pi*n)). - _Vaclav Kotesovec_, Jun 29 2013
%F A025577 Conjecture: (-n+1)*a(n) +3*(n-1)*a(n-1) +(n-7)*a(n-2) +3*(-n+3)*a(n-3)=0. - _R. J. Mathar_, Jul 02 2018
%t A025577 CoefficientList[Series[(x/(1-x))Sqrt[(1+x)/(1-3x)],{x,0,30}],x] (* _Harvey P. Dale_, Oct 17 2016 *)
%o A025577 (PARI) x='x+O('x^50); Vec((x/(1-x))*sqrt((1+x)/(1-3*x))) \\ _G. C. Greubel_, Feb 15 2017
%Y A025577 Sum{T(k, k-1), k = 1, 2, ..., n}, where T is the array defined in A025564.
%Y A025577 Partial sums of A025565.
%K A025577 nonn
%O A025577 1,2
%A A025577 _Clark Kimberling_
%E A025577 G.f. from _Vladeta Jovovic_, Jan 17 2004