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A212105
Number of (w,x,y,z) with all terms in {1,...,n} and w > harmonic mean of {x,y,z}.
3
0, 0, 7, 45, 150, 373, 768, 1437, 2479, 4002, 6120, 9010, 12786, 17661, 23821, 31464, 40809, 52102, 65577, 81531, 100201, 121911, 146979, 175717, 208434, 245550, 287401, 334380, 386877, 445366, 510222, 581922, 660952, 747750, 842850
OFFSET
0,3
COMMENTS
a(n)+A212104(n)=n^4.
A 4-tuple (w,x,y,z) is counted if 3/w>1/x+1/y+1/z.
For a guide to related sequences, see A211795.
MATHEMATICA
t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[w*(y*z + z*x + x*y) > 3 x*y*z, s = s + 1],
{w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];
Map[t[#] &, Range[0, 40]] (* A212105 *)
(* Peter J. C. Moses, Apr 13 2012 *)
CROSSREFS
Sequence in context: A262772 A153492 A107125 * A208826 A206808 A197369
KEYWORD
nonn
AUTHOR
Clark Kimberling, May 04 2012
STATUS
approved