The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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-François 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 12 10:54 EDT 2021. Contains 343821 sequences. (Running on oeis4.)