OFFSET
0,1
COMMENTS
If Y is a 4-subset of an n-set X then, for n>=12, a(n-12) is the number of 9-subsets of X having at most one element in common with Y. - Milan Janjic, Dec 08 2007
FORMULA
G.f.: (4-3*x)/(1-x)^10.
a(n) = 4*b(n)-3*b(n-1) =(n+36)*binomial(n+8, 8)/9, with b(n):=binomial(n+9, 9)=A000582(n+9, 9).
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Jun 11 2004
STATUS
approved