OFFSET
1,1
COMMENTS
See A157704 for background information.
FORMULA
a(n) = 7*a(n-1)-21*a(n-2)+35*a(n-3)-35*a(n-4)+21*a(n-5)-7*a(n-6)+a(n-7)
a(n) = 1/4*n^6+7/4*n^5+37/8*n^4+34/6*n^3+25/8*n^2+7/12*n
G.f.: (16 + 93*z + 66*z^2 + 5*z^3)/(1-z)^7
MAPLE
nmax:=24; for n from 0 to nmax do fz(n):=product((1-(k+1)*z)^(1+3*k), k=0..n); c(n):= coeff(fz(n), z, 2)/2; end do: a:=n-> c(n): seq(a(n), n=1..nmax);
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Johannes W. Meijer, Mar 07 2009
STATUS
approved