OFFSET
0,3
COMMENTS
Created in an attempt to repair a formula in A045996, which however turned out to be correct after all.
LINKS
Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).
FORMULA
a(n) = A099764(n-1) - 2*Sum_{l=2..n}Sum_{k=2..n}(n-k+1)*(n-l+1)*(k-1)*(l-1) = A099764(n-1)/9 = 4*A001249(n-2). - R. J. Mathar, May 23 2010
G.f.: 4*x^2*(1+x)*(x^2+8*x+1)/(1-x)^7. - R. J. Mathar, May 23 2010
MATHEMATICA
f[n_] := ((n - 1)^2*n^2*(n + 1)^2)/6 - 2*Sum[(n - k + 1)*(n - l + 1)*(k - 1) (l - 1), {k, 2, n}, {l, 2, n}]; Array[f, 31] (* Robert G. Wilson v, May 23 2010 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, May 19 2010, May 22 2010
STATUS
approved