OFFSET
0,2
REFERENCES
R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.65(a).
MAPLE
A131237 := proc(n)
exp((x*y*(3-x*y)/2+(x+y)*(2-x*y)/2)/(1-x*y))/sqrt(1-x*y) ;
coeftayl(%, y=0, n+1) ;
coeftayl(%, x=0, n) ;
%*(n+1)!*n! ;
simplify(%) ;
end proc: # R. J. Mathar, Sep 30 2011
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Vladeta Jovovic, Jun 20 2007
STATUS
approved