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 A026617 #12 Aug 06 2024 00:03:38
%S A026617 1,7,26,97,364,1374,5214,19877,76076,292162,1125332,4345642,16819256,
%T A026617 65226620,253403190,986022765,3842200140,14991031770,58558504620,
%U A026617 228986816190,896300806440,3511441192740
%N A026617 a(n) = A026615(2*n, n-1).
%H A026617 G. C. Greubel, <a href="/A026617/b026617.txt">Table of n, a(n) for n = 1..1000</a>
%F A026617 From _G. C. Greubel_, Jun 13 2024: (Start)
%F A026617 a(n) = (7*n^2 - 4*n + 1)*binomial(2*n-3, n-2)/binomial(n+1, 2) - 3*[n= 1].
%F A026617 G.f.: ( 2 - 5*x + 2*x^2 - (2 - x + 2*x^2)*sqrt(1 - 4*x) )/(2*x*sqrt(1-4*x)).
%F A026617 E.g.f.: (1/2)*( (1 - 2*x) - (1 - 2*x)*exp(2*x)*BesselI(0, 2*x) + 2*(2 - x)*exp(2*x)*BesselI(1, 2*x) ). (End)
%t A026617 Table[(7*n^2-4*n+1)*Binomial[2*n-3, n-2]/Binomial[n+1,2] - 3*Boole[n== 1], {n, 40}] (* _G. C. Greubel_, Jun 13 2024 *)
%o A026617 (Magma) [n eq 1 select 1 else (7*n^2-4*n+1)*Binomial(2*n-3, n-2)/Binomial(n+1, 2): n in [1..40]]; // _G. C. Greubel_, Jun 13 2024
%o A026617 (SageMath) [(7*n^2-4*n+1)*binomial(2*n-3, n-2)/binomial(n+1, 2) - 3*int(n==1) for n in range(1,41)] # _G. C. Greubel_, Jun 13 2024
%Y A026617 Cf. A026615, A026616, A026618, A026619, A026620, A026621, A026622.
%Y A026617 Cf. A026623, A026624, A026625, A026956, A026957, A026958, A026959.
%Y A026617 Cf. A026960, A176742.
%K A026617 nonn
%O A026617 1,2
%A A026617 _Clark Kimberling_