|
Search: id:A005263
|
|
|
| A005263 |
|
Number of labeled Greg trees.
(Formerly M3647)
|
|
+0
9
|
|
| 1, 1, 1, 4, 32, 396, 6692, 143816, 3756104, 115553024, 4093236352, 164098040448, 7345463787136, 363154251536896, 19653476190481408, 1155636468524067328, 73364615077878838784, 5001199614295920565248, 364363128390631094137856
(list; graph; listen)
|
|
|
OFFSET
|
0,4
|
|
|
COMMENT
|
A Greg tree can be described as a tree with 2-colored nodes where only the black nodes are counted and labeled and the white nodes are of degree at least 3.
|
|
REFERENCES
|
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
C. Flight, How many stemmata?, Manuscripta, 34 (1990), 122-128.
|
|
LINKS
|
Index entries for sequences related to trees
|
|
FORMULA
|
E.g.f.: 1+B(x)-B(x)^2 where B(x) is e.g.f. of A005264.
|
|
PROGRAM
|
(PARI) {a(n)= local(A); if(n<1, n==0, for(k= 1, n, A+= x*O(x^k); A= truncate( (1+x)* exp(A) -1-A) ); A+= x*O(x^n); A-= A^2; n!* polcoeff( A, n))} /* Michael Somos Apr 02 2007 */
|
|
CROSSREFS
|
Cf. A005264, A005640, A048159, A048160, A052300-A052303.
Sequence in context: A051489 A047053 A007763 this_sequence A113131 A127670 A005172
Adjacent sequences: A005260 A005261 A005262 this_sequence A005264 A005265 A005266
|
|
KEYWORD
|
nonn,nice,easy
|
|
AUTHOR
|
N. J. A. Sloane (njas(AT)research.att.com).
|
|
EXTENSIONS
|
More terms, formula and comment from Christian G. Bower (bowerc(AT)usa.net), Nov 15 1999.
|
|
|
Search completed in 0.002 seconds
|
