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A212109 Number of (w,x,y,z) with all terms in {1,...,n} and w*x-y*z<=n. 1
0, 1, 15, 69, 203, 467, 935, 1661, 2770, 4326, 6476, 9280, 13025, 17635, 23475, 30614, 39319, 49557, 61969, 76227, 93166, 112525, 134801, 159969, 189233, 221589, 258185, 299022, 344875, 395057, 451641, 512851, 580999, 655166, 736374 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

A212109(n)+A211060(n)=n^4.  For a guide to related sequences, see A211795.

LINKS

Table of n, a(n) for n=0..34.

MATHEMATICA

t = Compile[{{n, _Integer}}, Module[{s = 0},

(Do[If[w*x <= y*z + n, s = s + 1],

{w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];

Map[t[#] &, Range[0, 40]]   (* A212109 *)

(* Peter J. C. Moses, Apr 13 2012 *)

CROSSREFS

Cf. A211795, A211060.

Sequence in context: A015876 A201126 A085474 * A124893 A352941 A126402

Adjacent sequences:  A212106 A212107 A212108 * A212110 A212111 A212112

KEYWORD

nonn

AUTHOR

Clark Kimberling, May 07 2012

STATUS

approved

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Last modified September 27 22:01 EDT 2022. Contains 357063 sequences. (Running on oeis4.)