OFFSET
0,3
COMMENTS
For a guide to related sequences, see A212959.
LINKS
Index entries for linear recurrences with constant coefficients, signature (2,-1,0,1,-2,1).
FORMULA
a(n) = 2*a(n-1)-a(n-2)+a(n-4)-2*a(n-5)+a(n-6).
G.f.: f(x)/g(x), where f(x) = 1 - x + x^2 + x^3
and g(x) = (1 + x + x^2 + x^3)(1-x)^3.
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0}, (Do[If[4 w == x + y, s = s + 1], {w, 0, n}, {x, 0, n}, {y, 0, n}]; s)]];
m = Map[t[#] &, Range[0, 70]] (* A212988 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 04 2012
STATUS
approved