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 A372884 #10 May 17 2024 01:43:30
%S A372884 1,5,19,67,230,778,2602,8618,28303,92275,298949,963253,3089020,
%T A372884 9864896,31388260,99545572,314779181,992765041,3123577735,9806581175,
%U A372884 30727287586,96104495110,300081382574,935547839662,2912554595035,9055397013503,28119390725977,87217771234633
%N A372884 a(n) is the sum of all symmetric peaks in the set of flattened Catalan words of length n.
%H A372884 Jean-Luc Baril, Pamela E. Harris, and José L. Ramírez, <a href="https://arxiv.org/abs/2405.05357">Flattened Catalan Words</a>, arXiv:2405.05357 [math.CO], 2024. See p. 22.
%H A372884 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (9,-30,46,-33,9).
%F A372884 From Baril et al.: (Start)
%F A372884 G.f.: (1 - 2*x)^2*x^3/((1 - 3*x)^2*(1 - x)^3).
%F A372884 a(n) = (63 + 3^n + 2*(3^n - 45)*n + 18*n^2)/144. (End)
%F A372884 E.g.f.: (exp(3*x)*(1 + 6*x) + 9*exp(x)*(7 - 8*x + 2*x^2) - 64)/144.
%t A372884 LinearRecurrence[{9,-30,46,-33,9},{1,5,19,67,230},28]
%Y A372884 Cf. A372879, A372883.
%K A372884 nonn,easy
%O A372884 3,2
%A A372884 _Stefano Spezia_, May 15 2024