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Number of quasi series-parallel matroids on [n].
4

%I #8 Oct 15 2024 15:07:19

%S 1,2,5,16,67,374,2795,27472,343129,5242178,94775045,1976279584,

%T 46619596363,1225918376726,35526110971595,1124201803439968,

%U 38555828073355441,1424165085382532162,56356111920073052165,2378150844047351691376,106590791633357076443347

%N Number of quasi series-parallel matroids on [n].

%C A quasi series-parallel matroid is a collection of series-parallel matroids. See the Ferroni/Larson reference for a precise definition.

%H Andrew Howroyd, <a href="/A359986/b359986.txt">Table of n, a(n) for n = 0..200</a>

%H Luis Ferroni and Matt Larson, <a href="https://arxiv.org/abs/2303.02253">Kazhdan-Lusztig polynomials of braid matroids</a>, arXiv:2303.02253 [math.CO], 2023.

%o (PARI) seq(n)=Vec(serlaplace( exp(2*x + intformal(serreverse(2*log(1 + x + O(x^n)) - x))) ))

%o (PARI) seq(n) = Vec(serlaplace( exp(2*x + intformal(-x + 2*serreverse(1 + 2*x - exp(x + O(x^n))))) ))

%Y Row sums of A359985.

%K nonn

%O 0,2

%A _Andrew Howroyd_, Mar 08 2023