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 A026618 #9 Jun 17 2024 07:07:55
%S A026618 1,11,50,212,870,3509,14014,55640,220116,868870,3425092,13491064,
%T A026618 53117350,209097945,823111350,3240499440,12759776700,50254414650,
%U A026618 197979380220,780170359800,3075303389340
%N A026618 a(n) = A026618(2*n, n-2).
%H A026618 G. C. Greubel, <a href="/A026618/b026618.txt">Table of n, a(n) for n = 2..1000</a>
%F A026618 From _G. C. Greubel_, Jun 13 2024: (Start)
%F A026618 a(n) = (7*n^2 - 4*n + 4)*binomial(2*n, n-2)/(2*binomial(2*n, 2)) -[n=2].
%F A026618 G.f.: ( (2 - 9*x + 8*x^2 - 2*x^3) - (2 - 5*x + 2*x^2 + 2*x^4)*sqrt(1 - 4*x) )/(2*x^2*sqrt(1-4*x)).
%F A026618 E.g.f.: exp(2*x)*( (3 - x)*BesselI(0, 2*x) + (x - 1 - 2/x)*BesselI(1, 2*x) ) - (1 + x^2/2). (End)
%t A026618 Table[(7*n^2-4*n+4)*Binomial[2*n,n-2]/(2*Binomial[2*n,2]) -Boole[n==2], {n,2,40}] (* _G. C. Greubel_, Jun 13 2024 *)
%o A026618 (Magma) [n eq 2 select 1 else (7*n^2-4*n+4)*Binomial(2*n,n-2)/(2*Binomial(2*n,2)): n in [2..40]]; // _G. C. Greubel_, Jun 13 2024
%o A026618 (SageMath) [(7*n^2-4*n+4)*binomial(2*n, n-2)/(2*binomial(2*n, 2)) - int(n==2) for n in range(2,41)] # _G. C. Greubel_, Jun 13 2024
%Y A026618 Cf. A026615, A026616, A026617, A026619, A026620, A026621, A026622.
%Y A026618 Cf. A026623, A026624, A026625, A026956, A026957, A026958, A026959.
%Y A026618 Cf. A026960.
%K A026618 nonn
%O A026618 2,2
%A A026618 _Clark Kimberling_