OFFSET
0,2
COMMENTS
For a guide to related sequences, see A211422.
FORMULA
Conjectures from Colin Barker, May 15 2017: (Start)
G.f.: (1 + 2*x + 2*x^2 + 12*x^3 + 2*x^4 + 2*x^5 + x^6) / ((1 - x)^3*(1 + x + x^2)^2).
a(n) = a(n-1) + 2*a(n-3) - 2*a(n-4) - a(n-6) + a(n-7) for n>6.
(End)
MATHEMATICA
t[n_] := t[n] = Flatten[Table[w + 3 x + 3 y, {w, -n, n}, {x, -n, n}, {y, -n, n}]]
c[n_] := Count[t[n], 0]
t = Table[c[n], {n, 0, 70}] (* A211439 *)
(t - 1)/2 (* integers *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Clark Kimberling, Apr 11 2012
STATUS
approved