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A212019 Number of (w,x,y,z) with all terms in {1,...,n} and w*x=2*y*z. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

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

LINKS

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

EXAMPLE

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

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 *)

CROSSREFS

Cf. A211795.

Sequence in context: A277291 A254731 A291548 * A075708 A066617 A272272

Adjacent sequences:  A212016 A212017 A212018 * A212020 A212021 A212022

KEYWORD

nonn

AUTHOR

Clark Kimberling, Apr 28 2012

STATUS

approved

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Last modified July 20 14:01 EDT 2019. Contains 325181 sequences. (Running on oeis4.)