OFFSET
0,3
LINKS
Index entries for linear recurrences with constant coefficients, signature (4,-6,5,-5,6,-4,1).
FORMULA
a(n) = 4*a(n-1)-6*a(n-2)+5*a(n-3)-5*a(n-4)+6*a(n-5)-4*a(n-6)+a(n-7).
G.f.: x^2*(4+2*x+6*x^2+x^3)/((1+x+x^2)*(1-x)^5). [Bruno Berselli, Jun 05 2012]
a(n) = (13*n^4+10*n^3-5*n^2+6*n+8*b)/72, where b = 0,-3,1,0,-3,1,... (repeated). [Bruno Berselli, Jun 05 2012]
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[3 w >= x + y + z + n, s = s + 1],
{w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];
Map[t[#] &, Range[0, 40]] (* A212250 *)
(* Peter J. C. Moses, Apr 13 2012 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, May 09 2012
STATUS
approved