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 A212504 Number of (w,x,y,z) with all terms in {1,...,n} and w<2x and y>2z. 2
 0, 0, 0, 7, 24, 76, 162, 333, 576, 976, 1500, 2275, 3240, 4572, 6174, 8281, 10752, 13888, 17496, 21951, 27000, 33100, 39930, 48037, 57024, 67536, 79092, 92443, 107016, 123676, 141750, 162225, 184320, 209152, 235824, 265591, 297432 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS For a guide to related sequences, see A211795. LINKS Index entries for linear recurrences with constant coefficients, signature (2,2,-6,0,6,-2,-2,1). FORMULA a(n) = 2a(n-1)+2a(n-2)-6a(n-3)+6a(n-5)-2a(n-6)-2a(n-7)+a(n-8). From Alois P. Heinz, May 31 2012: (Start) a(n) = A077043(n) * A002620(n-1) = ceiling(n^2*3/4) * floor((n-1)^2/4). G.f.: x^3*(7+10*x+14*x^2+4*x^3+x^4) / ((x+1)^3*(1-x)^5). (End) MAPLE A212504:=n->ceil(3*n^2/4)*floor((n-1)^2/4); seq(A212504(n), n=0..40); # Wesley Ivan Hurt, Jan 24 2014 MATHEMATICA t = Compile[{{n, _Integer}}, Module[{s = 0}, (Do[If[w < 2 x && y > 2 z, s = s + 1], {w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]]; Map[t[#] &, Range[0, 40]]   (* A212504 *) CROSSREFS Cf. A211795. Sequence in context: A211381 A305676 A101903 * A196349 A196352 A050191 Adjacent sequences:  A212501 A212502 A212503 * A212505 A212506 A212507 KEYWORD nonn,easy AUTHOR Clark Kimberling, May 19 2012 STATUS approved

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Last modified April 26 04:11 EDT 2019. Contains 322469 sequences. (Running on oeis4.)