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 A054122 #20 Jan 26 2022 10:10:57
%S A054122 1,3,18,114,750,5058,34692,240852,1687446,11906610,84490428,602335836,
%T A054122 4310670156,30950436468,222844189320,1608369633384,11632913018598,
%U A054122 84294762019218,611831430746124,4447397950230540
%N A054122 T(2n,n), array T as in A054120.
%H A054122 Vincenzo Librandi, <a href="/A054122/b054122.txt">Table of n, a(n) for n = 0..200</a>
%F A054122 a(n) = A069835(n) - A069835(n-1).
%F A054122 G.f.: (1-x)/sqrt(1-8*x+4*x^2). - _Vladeta Jovovic_, May 13 2003
%F A054122 D-finite with recurrence: (n-1)*n*a(n) = 4*(n-1)*(2*n-1)*a(n-1) - 4*(n-2)*n*a(n-2). - _Vaclav Kotesovec_, Oct 09 2012
%F A054122 a(n) ~ sqrt(6+4*sqrt(3))*(4+2*sqrt(3))^n/(4*sqrt(Pi*n)). - _Vaclav Kotesovec_, Oct 09 2012
%F A054122 D-finite with recurrence n*a(n) +3*(-3*n+2)*a(n-1) +12*(n-2)*a(n-2) +4*(-n+3)*a(n-3)=0. - _R. J. Mathar_, Jun 13 2013
%t A054122 Table[SeriesCoefficient[(1-x)/Sqrt[1-8*x+4*x^2],{x,0,n}],{n,0,20}] (* _Vaclav Kotesovec_, Oct 09 2012 *)
%o A054122 (PARI) a(n)=(2*pollegendre(n,2) - pollegendre(n-1,2))<<(n-1) \\ _Charles R Greathouse IV_, Mar 18 2017
%Y A054122 Cf. A069835.
%K A054122 nonn
%O A054122 0,2
%A A054122 _Clark Kimberling_