|
Search: id:A111637
|
|
|
| A111637 |
|
Number of labeled graphs having n blue nodes and n green ones, where edges join only nodes of different colors. |
|
+0
2
|
|
| 1, 4, 96, 10240, 4587520, 8455716864, 63496796504064, 1932044240141942784, 237409596228641929297920, 117555946699326540948428554240, 234206054295766751302924897412448256
(list; graph; listen)
|
|
|
OFFSET
|
0,2
|
|
|
COMMENT
|
a(n)=A111636(2n,n).
|
|
REFERENCES
|
H. S. Wilf, Generatingfunctionology, 2nd edn., Academic Press, NY, 1994, p. 88.
|
|
FORMULA
|
a(n)=C(2n, n)*2^(n^2).
|
|
EXAMPLE
|
a(1)=4 because we have B G, B--G, G B, and G--B, where B (G) stands for a blue (green) node and -- denotes an edge.
|
|
MAPLE
|
a:=n->2^(n^2)*binomial(2*n, n): seq(a(n), n=0..12);
|
|
CROSSREFS
|
Cf. A111636.
Sequence in context: A013042 A065140 A007106 this_sequence A027872 A098695 A059201
Adjacent sequences: A111634 A111635 A111636 this_sequence A111638 A111639 A111640
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 09 2005
|
|
|
Search completed in 0.002 seconds
|
