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 A367056 #13 Dec 04 2023 05:33:00
%S A367056 1,1,2,6,17,52,168,561,1922,6719,23871,85938,312823,1149421,4257460,
%T A367056 15880036,59594517,224856450,852491806,3245959002,12407332166,
%U A367056 47592364107,183139542306,706794663136,2735053815771,10609811267757,41251228784198
%N A367056 G.f. satisfies A(x) = 1 + x*A(x)^2 + x^3*A(x).
%F A367056 G.f.: A(x) = 2 / (1-x^3+sqrt((1-x^3)^2-4*x)).
%F A367056 a(n) = Sum_{k=0..floor(n/3)} binomial(n-2*k+1,k) * binomial(2*n-5*k,n-3*k)/(n-2*k+1).
%F A367056 D-finite with recurrence (n+1)*a(n) +2*(-2*n+1)*a(n-1) +(-2*n+7)*a(n-3) +(n-8)*a(n-6)=0. - _R. J. Mathar_, Dec 04 2023
%p A367056 A367056 := proc(n)
%p A367056 add(binomial(n-2*k+1,k) * binomial(2*n-5*k,n-3*k)/(n-2*k+1),k=0..floor(n/3)) ;
%p A367056 end proc:
%p A367056 seq(A367056(n),n=0..70) ; # _R. J. Mathar_, Dec 04 2023
%o A367056 (PARI) a(n) = sum(k=0, n\3, binomial(n-2*k+1, k)*binomial(2*n-5*k, n-3*k)/(n-2*k+1));
%Y A367056 Cf. A049140, A071969, A125305, A216490, A367042.
%K A367056 nonn
%O A367056 0,3
%A A367056 _Seiichi Manyama_, Nov 04 2023