OFFSET
0,1
COMMENTS
If Y is a 3-subset of an n-set X then, for n>=6, a(n-6) is the number of 4-subsets of X having at most one element in common with Y. - Milan Janjic, Nov 23 2007
Row 3 of the convolution array A213550. [Clark Kimberling, Jun 20 2012]
FORMULA
G.f.: (3-2*x)/(1-x)^5.
a(n)= (n+12)*binomial(n+3, 3)/4 = 3*b(n)-2*b(n-1), with b(n):=binomial(n+4, 4); cf. A000332.
a(n) = sum_{k=1..n} ( sum_{i=1..k} i*(n-k+3) ), with offset 1. - Wesley Ivan Hurt, Sep 25 2013
MAPLE
MATHEMATICA
s1=s2=s3=s4=0; lst={}; Do[a=n+(n+2); s1+=a; s2+=s1; s3+=s2; s4+=s3; AppendTo[lst, s3/2], {n, 2, 5!}]; lst (* Vladimir Joseph Stephan Orlovsky, Apr 04 2009 *)
Table[(n+12)Binomial[n+3, 3)/4, {n, 0, 50}] (* Wesley Ivan Hurt, Oct 10 2013 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Jun 11 2004
STATUS
approved