A210587 -id:A210587 - cp's OEIS frontend

A030019 Number of labeled spanning trees in the complete hypergraph on n vertices (all hyperedges having cardinality 2 or greater).

1, 1, 1, 4, 29, 311, 4447, 79745, 1722681, 43578820, 1264185051, 41381702275, 1509114454597, 60681141052273, 2667370764248023, 127258109992533616, 6549338612837162225, 361680134713529977507, 21333858798449021030515, 1338681172839439064846881

Offset: 0

David Warme (warme(AT)s3i.com)

Equivalently, this is the number of "hypertrees" on n labeled nodes, i.e. connected hypergraphs that have no cycles, assuming that each edge contains at least two vertices. - Don Knuth, Jan 26 2008. See A134954 for hyperforests.
Also number of labeled connected graphs where every block is a complete graph (cf. A035053).
Let H = (V,E) be the complete hypergraph on N labeled vertices (all edges having cardinality 2 or greater). Let e in E and K = |e|. Then the number of distinct spanning trees of H that contain edge e is g(N,K) = K * E[X_N^{N-K}] / N and the K=1 case gives this sequence. Clearly there is some deep structural connection between spanning trees in hypergraphs and Poisson moments.

Warren D. Smith and David Warme, Paper in preparation, 2002.

Alois P. Heinz, Table of n, a(n) for n = 0..370 (first 101 terms from T. D. Noe)
Ayomikun Adeniran and Catherine Yan, Gončarov Polynomials in Partition Lattices and Exponential Families, arXiv:1907.07814 [math.CO], 2019.
Roland Bacher, On the enumeration of labelled hypertrees and of labelled bipartite trees, arXiv:1102.2708 [math.CO], 2011.
Maryam Bahrani and Jérémie Lumbroso, Enumerations, Forbidden Subgraph Characterizations, and the Split-Decomposition, arXiv:1608.01465 [math.CO], 2016.
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 810.
Louis H. Kalikow, Enumeration of parking functions, allowable permutation pairs, and labeled trees, PhD thesis, Brandeis University, 1999.
R. Lorentz, S. Tringali, and C.H. Yan, Generalized Goncarov polynomials, arXiv preprint arXiv:1511.04039, 2015.
Adam Piggott, The symmetries of Mccullough-Miller space, 2011, preprint.
Adam Piggott, The symmetries of Mccullough-Miller space, Algebra and Discrete Mathematics 14(2) (2012), 239-266.
D. M. Warme, Spanning Trees in Hypergraphs with Applications to Steiner Trees, PhD thesis, University of Virginia, 1998, Table 5.1.
D. M. Warme, Spanning Trees in Hypergraphs with Applications to Steiner Trees, PhD thesis, University of Virginia, 1998, Table 5.1.
Index entries for sequences related to trees

Cf. A030438, A035051, A035053, A134954, A134956, A134958. A052888, A210587.

a[n_] := Sum[ StirlingS2[n-1, i]*n^(i-1), {i, 0, n-1}]; a[0] = 1; Table[a[n], {n, 0, 18}](* Jean-François Alcover, Sep 12 2012, from 2nd formula *)

{a(n)=if(n==0,1,(n-1)!*polcoeff(1-sum(k=0, n-2, a(k+1)*x^k/k!*exp(-(k+1)*(exp(x+O(x^n))-1))), n-1))} /* Paul D. Hanna */

/* E.g.f. of sequence shifted left one place: */
{a(n)=local(A=1+x); for(i=1, n, A=exp(-1)*sum(m=0, 2*n+10, exp(m*x*A+x*O(x^n))/m!)); round(n!*polcoeff(A, n))} /* Paul D. Hanna */

a(n) = A035051(n)/n for n > 0.
a(n) = Sum_{i=0...n-1} Stirling2(n-1, i) n^(i-1), n >= 1. (Warme, Corollary 3.15.1, p. 59)
a(n) = E[X_n^{n-1}] / n, n >= 1, where X_n is a Poisson random variable with mean n.
1 = Sum_{n>=0} a(n+1) * x^n/n! * exp( -(n+1)*(exp(x)-1) ). - Paul D. Hanna, Jun 11 2011
E.g.f. satisfies: A(x) = Sum_{n>=0} exp(n*x*A(x)-1)/n! = Sum_{n>=0} a(n+1)*x^n/n!. - Paul D. Hanna, Sep 25 2011
Dobinski-type formula: a(n) = 1/e^n*sum {k = 0..inf} n^(k-1)*k^(n-1)/k!. Cf. A052888. For a refinement of this sequence see A210587. - Peter Bala, Apr 05 2012
a(n) ~ n^(n-2) / (sqrt(1+LambertW(1)) * (LambertW(1))^(n-1) * exp((2-1/LambertW(1))*n)). - Vaclav Kotesovec, Jul 26 2014

More terms, formula and comment from Christian G. Bower Dec 15 1999

A210586 Triangle T(n,k) read by rows: T(n,k) is the number of rooted hypertrees on n labeled vertices with k hyperedges, n >= 2, k >= 1.

Original entry on oeis.org

2, 3, 9, 4, 48, 64, 5, 175, 750, 625, 6, 540, 5400, 12960, 7776, 7, 1519, 30870, 156065, 252105, 117649, 8, 4032, 154112, 1433600, 4587520, 5505024, 2097152, 9, 10287, 704214, 11160261, 62001450, 141363306, 133923132, 43046721, 10, 25500, 3025000, 77700000, 695100000, 2646000000, 4620000000, 3600000000, 1000000000

Offset: 2

Peter Bala, Mar 26 2012

A hypergraph H is a pair (V,E) consisting of a finite set V of vertices and a set E of hyperedges given by subsets of V containing at least two elements. A walk in a hypergraph H connecting vertices v0 and vn is a sequence v0, e1, v1, e2, ... , v(n-1), en, vn, where each vi is in V and each ei is in E and for each ei the set {v(i-1),vi} is contained in ei. If for every pair of vertices v and v0 there is a walk in H starting at v and ending at v0 then H is called connected. A walk is a cycle if it contains at least two edges, all of the ei are distinct and all of the vi are distinct except v0 = vn. A connected hypergraph with no cycles is called a hypertree. A rooted hypertree is a hypertree in which one particular vertex is selected as being the root. For the enumeration of unrooted hypertrees see A210587.

			Triangle begins
.n\k.|....1.....2......3.......4.......5.......6
= = = = = = = = = = = = = = = = = = = = = = = = =
..2..|....2
..3..|....3.....9
..4..|....4....48.....64
..5..|....5...175....750.....625
..6..|....6...540...5400...12960....7776
..7..|....7..1519..30870..156065..252105..117649
...
Example of a hypertree with two hyperedges, one a 2-edge {3,4} and one a 3-edge {1,2,3}.
........__________........................
......./..........\.______................
......|....1...../.\......\...............
......|.........|.3.|....4.|..............
......|....2.....\./______/...............
.......\__________/.......................
..........................................
T(4,2) = 48. The twelve unrooted hypertrees on 4 vertices {1,2,3,4} with 2 hyperedges (one a 2-edge and one a 3-edge) have hyperedges:
{1,2,3} and {3,4}; {1,2,3} and {2,4}; {1,2,3} and {1,4};
{1,2,4} and {1,3}; {1,2,4} and {2,3}; {1,2,4} and {3,4};
{1,3,4} and {1,2}; {1,3,4} and {2,3}; {1,3,4} and {2,4};
{2,3,4} and {1,2}; {2,3,4} and {1,3}; {2,3,4} and {1,4}.
Choosing one of the four vertices as the root gives a total of 4x12 = 48 rooted hypertrees on 4 vertices.

Andrew Howroyd, Table of n, a(n) for n = 2..1276
Roland Bacher, On the enumeration of labelled hypertrees and of labelled bipartite trees, arXiv:1102.2708 [math.CO], 2011.
J. McCammond and J. Meier, The hypertree poset and the l^2-Betti numbers of the motion group of the trivial link, Mathematische Annalen 328 (2004), no. 4, 633-652.

Cf. A035051 (row sums). Cf. A210587, A048993.

with(combinat):
A210586 := (n, k) -> n^k*stirling2(n-1, k):
for n from 2 to 10 do seq(A210586(n, k), k = 1..n-1) end do;
# Peter Bala, Oct 28 2015

T(n,k) = {n^k*stirling(n-1,k,2)}
for(n=2, 10, for(k=1, n-1, print1(T(n, k), ", ")); print); \\ Andrew Howroyd, Aug 28 2018

T(n,k) = n^k*Stirling2(n-1,k). T(n,k) = n*A210587(n,k).
E.g.f. A(x,t) = t + 2*x*t^2/2! + (3*x + 9*x^2)*t^3/3! + ... satisfies A(x,t) = t*exp(x*(exp(A(x,t)) - 1)).
Dobinski-type formula for the row polynomials: R(n,x) = exp(-n*x)*Sum_{k = 0..inf} n^k*k^(n-1)x^k/k!.
Row sums A035051.
The e.g.f. is essentially the series reversion of t/F(x,t) w.r.t. t, where F(x,t) = exp(x*(exp(t) - 1)) is the e.g.f. of the Stirling numbers of the second kind A048993. - Peter Bala, Oct 28 2015

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A030019 Number of labeled spanning trees in the complete hypergraph on n vertices (all hyperedges having cardinality 2 or greater).

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A210586 Triangle T(n,k) read by rows: T(n,k) is the number of rooted hypertrees on n labeled vertices with k hyperedges, n >= 2, k >= 1.

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