OFFSET
0,4
COMMENTS
For a guide to related sequences, see A211795.
LINKS
Index entries for linear recurrences with constant coefficients, signature (2,2,-6,0,6,-2,-2,1).
FORMULA
a(n) = 2a(n-1)+2a(n-2)-6a(n-3)+6a(n-5)-2a(n-6)-2a(n-7)+a(n-8).
From Alois P. Heinz, May 31 2012: (Start)
G.f.: x^3*(7+10*x+14*x^2+4*x^3+x^4) / ((x+1)^3*(1-x)^5). (End)
MAPLE
A212504:=n->ceil(3*n^2/4)*floor((n-1)^2/4); seq(A212504(n), n=0..40); # Wesley Ivan Hurt, Jan 24 2014
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[w < 2 x && y > 2 z, s = s + 1],
{w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];
Map[t[#] &, Range[0, 40]] (* A212504 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, May 19 2012
STATUS
approved