OFFSET
1,3
COMMENTS
For a guide to related sequences, see A212959.
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.: (x + 3*x^2 + x^3)/((1 + x)*(1 - x)^4).
From Ayoub Saber Rguez, Oct 08 2021: (Start)
a(n) = (10*n^3 + 15*n^2 + 2*n - 3 + 3*((n+1) mod 2))/24. (End)
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[w < x + y && x < y, s = s + 1],
{w, 0, n}, {x, 0, n}, {y, 0, n}]; s)]];
m = Map[t[#] &, Range[0, 60]] (* A212980 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 03 2012
STATUS
approved