OFFSET
0,1
COMMENTS
If Y is a 5-subset of an n-set X then, for n>=9, a(n-9) is the number of 5-subsets of X having at most one element in common with Y. - Milan Janjic, Dec 08 2007
LINKS
Index entries for linear recurrences with constant coefficients, signature (6, -15, 20, -15, 6, -1).
FORMULA
G.f.: (5-4*x)/(1-x)^6.
a(n)= (n+25)*binomial(n+4, 4)/5 = 5*b(n)-4*b(n-1), with b(n):= A000389(n+5)=binomial(n+5, 5).
a(0)=5, a(1)=26, a(2)=81, a(3)=196, a(4)=406, a(5)=756, a(n)=6*a(n-1)- 15*a(n-2)+20*a(n-3)-15*a(n-4)+6*a(n-5)-a(n-6). - Harvey P. Dale, Jan 11 2014
MATHEMATICA
CoefficientList[Series[(5-4x)/(1-x)^6, {x, 0, 40}], x] (* or *) LinearRecurrence[ {6, -15, 20, -15, 6, -1}, {5, 26, 81, 196, 406, 756}, 40] (* Harvey P. Dale, Jan 11 2014 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Jul 16 2004
STATUS
approved