OFFSET
0,4
COMMENTS
For a guide to related sequences, see A211795.
LINKS
Index entries for linear recurrences with constant coefficients, signature (3, -3, 2, -3, 3, -1).
FORMULA
a(n)=3*a(n-1)-3*a(n-2)+2*a(n-3)-3*a(n-4)+3*a(n-5)-a(n-6).
G.f.: (x^2 + 4*x^3 + 3*x^4 + 2*x^5)/(1 - 3*x + 3* x^2 - 2*x^3 + 3*x^4 - 3*x^5 + x^6)
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[w + y == Abs[x - y] + Abs[y - z], s = s + 1],
{w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];
Map[t[#] &, Range[0, 40]] (* A212677 *)
LinearRecurrence[{3, -3, 2, -3, 3, -1}, {0, 0, 1, 7, 21, 46}, 40]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, May 23 2012
STATUS
approved