A211809 Number of 4-tuples (w,x,y,z) with all terms in {1,...,n} and w*x >= 2*y*z.

0, 0, 5, 23, 79, 188, 402, 742, 1283, 2059, 3164, 4633, 6615, 9112, 12299, 16253, 21114, 26924, 33932, 42161, 51885, 63153, 76182, 91068, 108172, 127453, 149257, 173726, 201163, 231591, 265520, 302889, 344195, 389508, 439180, 493458

Offset: 0

Author

Clark Kimberling, Apr 27 2012

Keywords

• nonn

Comments

a(n) + A211795(n) = n^4.

See A211795 for a guide to related sequences.

Links

• Bo Gyu Jeong, Table of n, a(n) for n = 0..200

Crossrefs

Cf. A211795.

Programs

Mathematica

t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[w*x >= 2 y*z, s = s + 1],
{w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];
Map[t[#] &, Range[0, 40]] (* A211809 *)
(* Peter J. C. Moses, Apr 13 2012 *)