A212019 Number of (w,x,y,z) with all terms in {1,...,n} and w*x=2*y*z.

0, 0, 4, 8, 24, 32, 64, 76, 124, 154, 214, 234, 340, 364, 452, 532, 664, 696, 854, 890, 1086, 1206, 1350, 1394, 1692, 1794, 1966, 2108, 2396, 2452, 2822, 2882, 3212, 3408, 3636, 3860, 4360, 4432, 4688, 4920, 5470, 5550, 6090, 6174, 6642, 7056

Offset: 0

Author

Clark Kimberling, Apr 28 2012

Keywords

• nonn

Comments

Each term is divisible by 2. See A211795 for a guide to related sequences.

Examples

			a(2) counts these four 4-tuples: (1,2,1,1), (2,1,1,1), (2,2,1,2), (2,2,2,1).
		

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, 60]] (* A212019 *)
%/2  (* integers *)
(* Peter J. C. Moses, Apr 13 2012 *)