cp's OEIS Frontend

A213390 Number of (w,x,y) with all terms in {0,...,n} and max(w,x,y) >= 2*min(w,x,y).

%I A213390 #14 Jun 18 2017 02:26:45
%S A213390 1,7,25,55,109,181,289,421,601,811,1081,1387,1765,2185,2689,3241,3889,
%T A213390 4591,5401,6271,7261,8317,9505,10765,12169,13651,15289,17011,18901,
%U A213390 20881,23041,25297,27745,30295,33049,35911,38989,42181,45601
%N A213390 Number of (w,x,y) with all terms in {0,...,n} and max(w,x,y) >= 2*min(w,x,y).
%C A213390 a(n)+A213389(n) = (n+1)^3.
%C A213390 For a guide to related sequences, see A212959.
%H A213390 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,-4,1,2,-1).
%F A213390 a(n) = 2*a(n-1)+a(n-2)-4*a(n-3)+a(n-4)+2*a(n-5)-a(n-6).
%F A213390 G.f.: (1 + 5*x + 10*x^2 + 2*x^3 + x^4 - x^5)/((1 - x)^4*(1 + x)^2).
%F A213390 a(n) = (6*n^3+24*n^2+21*n+8+3*n*(-1)^n)/8. - _Luce ETIENNE_, Jul 17 2016
%t A213390 t = Compile[{{n, _Integer}}, Module[{s = 0},
%t A213390 (Do[If[Max[w, x, y] >= 2*Min[w, x, y], s = s + 1],
%t A213390 {w, 0, n}, {x, 0, n}, {y, 0, n}]; s)]];
%t A213390 m = Map[t[#] &, Range[0, 50]]   (* A213390 *)
%Y A213390 Cf. A212959.
%K A213390 nonn,easy
%O A213390 0,2
%A A213390 _Clark Kimberling_, Jun 11 2012