OFFSET
0,2
COMMENTS
Every term is even.
LINKS
Index entries for linear recurrences with constant coefficients, signature (3,-2,-2,3,-1).
FORMULA
a(n) = 3*a(n-1) - 2*a(n-2) - 2*a(n-3) + 3*a(n-4) - a(n-5).
G.f.: 2*x*(2 + x + x^2)/((-1 + x)^4*(1 + x)).
a(n) = (n+1)^3 - A087035(n+1).
a(n) = 2*A212685(n+1) = (2*n*(4*n^2+9*n+8) - 3*(-1)^n + 3)/12. [Bruno Berselli, Jun 11 2012]
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0}, (Do[If[Max[w, x, y] - Min[w, x, y] < 2 Abs[w - x], s = s + 1], {w, 0, n}, {x, 0, n}, {y, 0, n}]; s)]];
m = Map[t[#] &, Range[0, 45]] (* this sequence *)
m/2 (* integers *)
LinearRecurrence[{3, -2, -2, 3, -1}, {0, 4, 14, 36, 72}, 50] (* Harvey P. Dale, Jul 31 2013 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 10 2012
STATUS
approved