|
|
A007827
|
|
Number of homeomorphically irreducible (or series-reduced) trees with n pendant nodes, or continua with n non-cut points, or leaves.
|
|
15
|
|
|
1, 1, 1, 1, 2, 3, 7, 13, 32, 73, 190, 488, 1350, 3741, 10765, 31311, 92949, 278840, 847511, 2599071, 8044399, 25082609, 78758786, 248803504, 790411028, 2523668997, 8095146289, 26076714609, 84329102797, 273694746208
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,5
|
|
COMMENTS
|
Also, number of unrooted multifurcating tree shapes with n leaves [see Felsenstein].
|
|
REFERENCES
|
M. Cropper, J. Combin. Math. Combin. Comp., Vol. 24 (1997), 177-184.
Joseph Felsenstein, Inferring Phylogenies. Sinauer Associates, Inc., 2004, p. 33 (Beware errors!).
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 62.
S. B. Nadler Jr., Continuum Theory, Academic Press.
|
|
LINKS
|
|
|
FORMULA
|
G.f.: 1+(1+x-B(x))*B(x) where B(x) = x+x^2+2*x^3+5*x^4+12*x^5+33*x^6+90*x^7+... is g.f. for A000669.
|
|
MAPLE
|
A := series(1+(1+x-B)*B, x, 30); # where B = g.f. for A000669; A007827 := n->coeff(A, x, n);
|
|
MATHEMATICA
|
(* a9 = A000669 *) max = 29; a9[1] = 1; a9[n_] := (s = Series[1/(1 - x), {x, 0, n}]; Do[s = Series[s/(1 - x^k)^Coefficient[s, x^k], {x, 0, n}], {k, 2, n}]; Coefficient[s, x^n]/2); b[x_] := Sum[a9[n] x^n, {n, 1, max}]; gf[x_] := 1 + (1 + x - b[x])*b[x]; CoefficientList[ Series[gf[x], {x, 0, max}], x] (* Jean-François Alcover, Aug 14 2012 *)
|
|
CROSSREFS
|
Cf. A000014 (series-reduced trees), A000055 (trees), A000311, A000669 (series-reduced planted trees by leaves), A059123 (homeomorphically irreducible rooted trees by nodes), A271205 (series-reduced trees by leaves and nodes).
|
|
KEYWORD
|
nonn,nice,easy
|
|
AUTHOR
|
Matthew Cropper (mmcrop01(AT)athena.louisville.edu).
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|