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 A047073 #16 May 11 2024 17:13:45
%S A047073 1,2,4,4,8,12,24,40,80,140,280,504,1008,1848,3696,6864,13728,25740,
%T A047073 51480,97240,194480,369512,739024,1410864,2821728,5408312,10816624,
%U A047073 20801200,41602400,80233200,160466400,310235040,620470080,1202160780
%N A047073 a(n) = Sum_{j=0..n} A047072(j, n-j).
%H A047073 G. C. Greubel, <a href="/A047073/b047073.txt">Table of n, a(n) for n = 0..1000</a>
%F A047073 a(n) = 2*A063886(n-1) + (n+1)*[n<2].
%F A047073 G.f.: 1 + 2*x*sqrt((1+2*x)/(1-2*x)). - _Michael Somos_
%F A047073 E.g.f.: 1 - x*BesselI(1, 2*x)*(2 + Pi*(1 + 2*x)*StruveL(0, 2*x)) + x*(1 + 2*x)*BesselI(0, 2*x)*(2 + Pi*StruveL(1, 2*x)). - _Stefano Spezia_, May 11 2024
%t A047073 Table[If[n<2, n+1, 4*Binomial[n-2, Floor[(n-2)/2]]], {n,0,40}] (* _G. C. Greubel_, Oct 13 2022 *)
%o A047073 (PARI) a(n) = if(n<2, max(0,n+1), 4*binomial(n-2, n\2-1))
%o A047073 (Magma) [n le 1 select n+1 else 4*Binomial(n-2, Floor((n-2)/2)): n in [0..40]]; // _G. C. Greubel_, Oct 13 2022
%o A047073 (SageMath) [4*binomial(n-2, ((n-2)//2)) + (n+1)*int(n<2) for n in range(41)] # _G. C. Greubel_, Oct 13 2022
%Y A047073 Cf. A047072, A063886.
%K A047073 nonn
%O A047073 0,2
%A A047073 _Clark Kimberling_