This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A001059 Number of labeled heap ordered trees. 2
 1, 1, 5, 59, 1263, 42713, 2094399, 140434335, 12340275539, 1375857855221, 189751578038547, 31714568837559539, 6316261763436325285, 1477890415844440910325, 401400487846091289175217, 125247016772173387008904623, 44493481073675052201518261955 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS A standard heap ordered tree with n + 1 nodes is a finite rooted tree in which all the nodes except the root are labeled with the natural numbers between 1 and n, which satisfies the property that the labels of the children of a node are all larger than the label of the node. LINKS T. D. Noe, Table of n, a(n) for n = 0..100 R. L. Grossman R. G. Larson, Hopf Algebras of Heap Ordered Trees and Permutations, arXiv:0706.1327v3 [math.RA] FORMULA zf"+f'=1/(1-f). a(n) = Sum_{k=0..n-1} binomial(n, k)^2*a(k)*a(n-k-1). - Vladeta Jovovic, Oct 22 2005 MATHEMATICA t = {1}; Do[AppendTo[t, Sum[Binomial[n, k]^2 t[[k+1]] t[[n-k]], {k, 0, n-1}]], {n, 20}] (* T. D. Noe, Jun 25 2012 *) CROSSREFS Sequence in context: A020468 A093946 A249519 * A290702 A326573 A324240 Adjacent sequences:  A001056 A001057 A001058 * A001060 A001061 A001062 KEYWORD nonn AUTHOR Helmut Prodinger [ Helmut.Prodinger(AT)inria.fr ] 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 December 6 04:14 EST 2019. Contains 329784 sequences. (Running on oeis4.)