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A213392
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Number of (w,x,y) with all terms in {0,...,n} and 2*max(w,x,y) >= 3*min(w,x,y).
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3
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1, 7, 25, 61, 115, 199, 319, 469, 667, 919, 1213, 1573, 2005, 2491, 3061, 3721, 4447, 5275, 6211, 7225, 8359, 9619, 10969, 12457, 14089, 15823, 17713, 19765, 21931, 24271, 26791, 29437, 32275, 35311, 38485, 41869, 45469, 49219, 53197
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OFFSET
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0,2
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COMMENTS
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For a guide to related sequences, see A212959.
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LINKS
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FORMULA
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a(n) = 2*a(n-1) - a(n-2) + 2*a(n-3) - 4*a(n-4) + 2*a(n-5) - a(n-6) + 2*a(n-7) - a(n-8).
G.f.: -(-1 - 5*x - x^6 - 12*x^2 - 16*x^3 - 8*x^4 - 6*x^5 + x^7) / ((x^2 + x + 1)^2*(x-1)^4).
a(n) = (8*n^3 + 27*n^2 + 21*n + 6*n*(((n+1) mod 3) mod 2) + 7 + 2*((2*n+1) mod 3))/9. (End)
a(n) = (8*n^3 + 27*n^2 + 27*n + 9)/9 if n == 0 (mod 3);
= (8*n^3 + 27*n^2 + 21*n + 7)/9 if n == 1 (mod 3);
= (8*n^3 + 27*n^2 + 21*n + 11)/9 if n == 2 (mod 3).
(End)
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MATHEMATICA
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t = Compile[{{n, _Integer}}, Module[{s = 0},
(Do[If[2*Max[w, x, y] >= 3*Min[w, x, y], s = s + 1],
{w, 0, n}, {x, 0, n}, {y, 0, n}]; s)]];
m = Map[t[#] &, Range[0, 45]] (* A213391 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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