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A212108 Number of (w,x,y,z) with all terms in {1,...,n} and w*x-y*z

%I A212108 #5 Dec 04 2016 19:46:29
%S A212108 0,1,13,62,187,444,885,1616,2677,4227,6326,9163,12742,17468,23167,
%T A212108 30278,38876,49268,61315,75858,92363,111867,134039,159426,187841,
%U A212108 220810,257093,297936,343312,394178,449481,511840,578961,653514,734486
%N A212108 Number of (w,x,y,z) with all terms in {1,...,n} and w*x-y*z<n.
%C A212108 A212108(n)+A211061(n)=n^4.  For a guide to related sequences, see A211795.
%t A212108 t = Compile[{{n, _Integer}}, Module[{s = 0},
%t A212108 (Do[If[w*x < y*z + n, s = s + 1],
%t A212108 {w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];
%t A212108 Map[t[#] &, Range[0, 40]]   (* A212108 *)
%t A212108 (* _Peter J. C. Moses_, Apr 13 2012 *)
%Y A212108 Cf. A211795, A211061.
%K A212108 nonn
%O A212108 0,3
%A A212108 _Clark Kimberling_, May 07 2012