OFFSET
0,4
COMMENTS
For a guide to related sequences, see A211422.
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (1,0,2,-2,0,-1,1).
FORMULA
a(n) = a(n-1) + 2*a(n-3) - 2*a(n-4) - a(n-6) + a(n-7).
G.f.: x^3*(2 + x + x^2 + x^3) / ((1 - x)^3*(1 + x + x^2)^2). - Colin Barker, Dec 03 2017
MATHEMATICA
t[n_] := t[n] = Flatten[Table[w - 3 x + 3 y, {w, 1, n}, {x, 1, n}, {y, 1, n}]]
c[n_] := Count[t[n], 0]
t = Table[c[n], {n, 0, 70}] (* A211546 *)
FindLinearRecurrence[t]
LinearRecurrence[{1, 0, 2, -2, 0, -1, 1}, {0, 0, 0, 2, 3, 4, 9}, 56] (* Ray Chandler, Aug 02 2015 *)
PROG
(PARI) concat(vector(3), Vec(x^3*(2 + x + x^2 + x^3) / ((1 - x)^3*(1 + x + x^2)^2) + O(x^40))) \\ Colin Barker, Dec 03 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Apr 15 2012
STATUS
approved