OFFSET
0,1
COMMENTS
If Y is a 5-subset of an n-set X then, for n>=7, a(n-7) is the number of 3-subsets of X having at most one element in common with Y. - Milan Janjic, Dec 08 2007
FORMULA
a(n)= (n+15)*(n+2)*(n+1)/6 = 5*b(n)-4*b(n-1), with b(n):=A000292(n)=binomial(n+3, 3).
G.f.: (5-4*x)/(1-x)^4.
MATHEMATICA
Table[(n^3 + 15 n^2 + 14 n)/6, {n, 100}] (* Vladimir Joseph Stephan Orlovsky, Jul 06 2011 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Jul 16 2004
STATUS
approved