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Consider the family of multigraphs enriched by the species of simple graphs. Sequence gives number of those multigraphs with n labeled edges.
2

%I #12 Jan 12 2021 20:48:31

%S 1,1,4,29,330,5438,128211,4808964,378829853,77137284917,

%T 36854103598061,36864364745783295,74684573193253556537,

%U 304187997559381840229969,2484431769481244742219110666,40639512967159110848931023115111,1330529956364528398902155692019721596

%N Consider the family of multigraphs enriched by the species of simple graphs. Sequence gives number of those multigraphs with n labeled edges.

%D G. Paquin, Dénombrement de multigraphes enrichis, Mémoire, Math. Dept., Univ. Québec à Montréal, 2004.

%H Andrew Howroyd, <a href="/A099700/b099700.txt">Table of n, a(n) for n = 0..50</a>

%H G. Paquin, <a href="/A038205/a038205.pdf">Dénombrement de multigraphes enrichis</a>, Mémoire, Math. Dept., Univ. Québec à Montréal, 2004. [Cached copy, with permission]

%F E.g.f.: B(R(x)) where B(x) is the e.g.f. of A014500 and 1 + R(x) is the e.g.f. of A006125. - _Andrew Howroyd_, Jan 12 2021

%o (PARI) \\ R(n) is A006125 as e.g.f.; EnrichedGnSeq defined in A098620.

%o R(n)={sum(k=0, n, 2^binomial(k,2)*x^k/k!) + O(x*x^n)}

%o EnrichedGnSeq(R(20)) \\ _Andrew Howroyd_, Jan 12 2021

%Y Cf. A006125, A014500, A098620, A099701, A099702, A099703.

%K nonn

%O 0,3

%A _N. J. A. Sloane_, Oct 26 2004

%E Terms a(12) and beyond from _Andrew Howroyd_, Jan 12 2021