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A339066 Number of unlabeled multigraphs with n edges rooted at two indistinguishable vertices. 2
1, 3, 12, 44, 171, 664, 2688, 11133, 47682, 210275, 955940, 4473128, 21532160, 106504216, 540824997, 2816636171, 15031261538, 82123830645, 458979942506, 2621982351176, 15298840540234, 91112889589166, 553492059017778, 3427579611162937, 21625096669854023, 138927108066308515 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..25.

EXAMPLE

The a(1) = 3 cases correspond to a single edge which can be attached to zero, one or both of the roots.

MATHEMATICA

seq[n_] := G[2n, x + O[x]^n, {1, 1}] + G[2n, x + O[x]^n, {2}] // CoefficientList[#/2, x]&;

seq[15] (* Jean-Fran├žois Alcover, Dec 02 2020, after Andrew Howroyd's code for G in A339065 *)

PROG

(PARI) \\ See A339065 for G.

seq(n)={my(A=O(x*x^n)); Vec((G(2*n, x+A, [1, 1]) + G(2*n, x+A, [2]))/2)}

CROSSREFS

Cf. A050535, A007717 (one root), A339043, A339064, A339065.

Sequence in context: A109437 A331473 A005656 * A260146 A229936 A258626

Adjacent sequences:  A339063 A339064 A339065 * A339067 A339068 A339069

KEYWORD

nonn

AUTHOR

Andrew Howroyd, Nov 22 2020

STATUS

approved

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Last modified April 17 08:40 EDT 2021. Contains 343064 sequences. (Running on oeis4.)