OFFSET
0,2
FORMULA
a(n)= A090216(n+2, 7)/600, n>=0.
a(n)= ((5!)^n)*(1-2*6^(n+1)+binomial(7, 2)^(n+1))/(2*5). From eq.12 of the Blasiak et al. reference given in A007840 with r=5=s, k=7.
a(n)= (21*(7*6*5*4*3)^n - 12*(6*5*4*3*2)^n + (5*4*3*2*1)^n)/10.
G.f.: (1+1080*x)/product(1-fallfac(p, 5)*x, p=5..7), with fallfac(n, m) := A008279(n, m) (falling factorials).
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Feb 13 2004
STATUS
approved