OFFSET
0,2
COMMENTS
For a guide to related sequences, see A212959.
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,0,2,-2,0,-1,1).
FORMULA
a(n) = a(n-1) + 2*a(n-3) - 2*a(n-4) - a(n-6) + a(n-7).
G.f.: f(x)/g(x), where f(x) = 1 + x + x^2 + 2*x^3 and g(x) = ((1+x+x^2)^2)*((1-x)^3).
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[3 w == 3 x + y, s = s + 1],
{w, 0, n}, {x, 0, n}, {y, 0, n}]; s)]];
m = Map[t[#] &, Range[0, 70]] (* A212985 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 04 2012
STATUS
approved