OFFSET
0,2
COMMENTS
FORMULA
a(n)=2*a(n-1)+2*a(n-2)-6*a(n-3)+6*a(n-5)-2*a(n-6)-2*a(n-7)+a(n-8).
G.f.: f(x)/g(x), where f(x)=-7*x-18*x^2-34*x^3-18*x^4-7*x^5 and g(x)=((1-x)^5)*(1+x)^3.
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[Max[w, x, y, z] > 2 Min[w, x, y, z], s = s + 1],
{w, 0, n}, {x, 0, n}, {y, 0, n}, {z, 0, n}]; s)]];
Map[t[#] &, Range[0, 40]] (* A212743 *)
%/2 (* integers *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, May 26 2012
STATUS
approved