A304071 -id:A304071 - cp's OEIS frontend

A303831 Birooted graphs: number of unlabeled connected graphs with n nodes rooted at 2 indistinguishable roots.

0, 1, 3, 16, 98, 879, 11260, 230505, 7949596, 483572280, 53011686200, 10589943940654, 3880959679322754, 2623201177625659987, 3286005731275218388682, 7663042204550840483139108, 33407704152242477510352455230, 273327599183687887638526170380380

Offset: 1

Brendan McKay, May 01 2018

nonn

Andrew Howroyd, Table of n, a(n) for n = 1..40
Jean-François Alcover, Mathematica program

Cf. A303829 (not necessarily connected). 3rd column of A304311.

Cf. A000088 (not rooted), A126100 (connected single root), A053506 (2 roots adjacent).

Mathematica
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G.f.: B(x)/G(x) - (C(x^2) + C(x)^2)/2 where B(x) is the g.f. of A303829, G(x) is the g.f. of A000088 and C(x) is the g.f. of A126100. - Andrew Howroyd, May 03 2018

a(n) = A303830(n) + A304071(n). - Brendan McKay, May 05 2018

a(12)-a(18) from Andrew Howroyd, May 03 2018

A304073 Number of simple connected graphs with n nodes rooted at one oriented non-edge.

Original entry on oeis.org

0, 0, 1, 8, 67, 701, 10047, 218083, 7758105, 478466565, 52762737260, 10566937121191, 3876933205880431, 2621875289142578194, 3285187439267316978728, 7662096100649423384254265, 33405651855362295512020765765, 273319227135047244053866187609854

Offset: 1

Brendan McKay, May 05 2018

nonn

			a(3)=1: no contribution from the triangle graph; one case of joining the leaves of the linear graph.
a(4)=8: we start from the 6 cases of non-oriented non-edges of A304071 and note two geometries where the orientation makes a difference: for the triangular graph with a protruding edge the orientation matters (to or from the leaf), and also for the linear graph with 4 nodes (to or from the leaf).

Andrew Howroyd, Table of n, a(n) for n = 1..50

Cf. A001349 (not rooted), A304069 (not necessarily connected).

Cf. A000088, A000666.

permcount(v) = {my(m=1, s=0, k=0, t); for(i=1, #v, t=v[i]; k=if(i>1&&t==v[i-1], k+1, 1); m*=t*k; s+=t); s!/m}
edges(v) = {sum(i=2, #v, sum(j=1, i-1, gcd(v[i], v[j]))) + sum(i=1, #v, v[i]\2)}
cross(u, v) = {sum(i=1, #u, sum(j=1, #v, gcd(u[i], v[j])))}
S(n, r)={my(t=#r+1); vector(n+1, n, if(nAndrew Howroyd, Sep 07 2019

a(n) + A304072(n) = A304074(n).

G.f.: B(x)/G(x) - (x*C(x)/G(x))^2, where B(x) is the g.f. of A304069, C(x) is the g.f. of A000666 and G(x) is the g.f. of A000088. - Andrew Howroyd, Sep 07 2019

Terms a(13) and beyond from Andrew Howroyd, Sep 07 2019

cp's OEIS Frontend

A303831 Birooted graphs: number of unlabeled connected graphs with n nodes rooted at 2 indistinguishable roots.

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