OFFSET
0,2
COMMENTS
For a guide to related sequences, see A212959.
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,3,-3,-3,3,1,-1).
FORMULA
a(n)=a(n-1)+3*a(n-2)-3*a(n-3)-3*a(n-4)+3*a(n-5)+a(n-6)-a(n-7).
G.f.: f(x)/g(x), where f(x)=3*x + 3*x^2 + x^3
and g(x)=((1+x)^3)(1-x)^4.
a(n) = (14*n^3+75*n^2+109*n-3*((n^2+7*n+11)*(-1)^n-11))/96. - Luce ETIENNE, Mar 21 2014
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[n/2 < w + x + y <= n, s = s + 1],
{w, 0, n}, {x, 0, n}, {y, 0, n}]; s)]];
m = Map[t[#] &, Range[0, 70]] (* A212977 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 04 2012
STATUS
approved