OFFSET
1,1
COMMENTS
See A157705 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) = 1/2*n^6+5/2*n^5+41/8*n^4+67/12*n^3+27/8*n^2+11/12*n
G.f.: (18 + 128*z + 171*z^2 + 42*z^3 + z^4)/(1-z)^7
MAPLE
nmax:=23; for n from 0 to nmax do fz(n):=product((1-(2*n+1-2*k)*z)^(3*k+1), k=0..n); c(n):= coeff(fz(n), z, 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