OFFSET
0,2
REFERENCES
H. S. Wilf, Generatingfunctionology, 2nd edn., Academic Press, NY, 1994, p. 88.
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
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Aug 09 2005
STATUS
approved