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A211546
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Number of ordered triples (w,x,y) with all terms in {1,...,n} and w=3x-3y.
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2
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0, 0, 0, 2, 3, 4, 9, 11, 13, 21, 24, 27, 38, 42, 46, 60, 65, 70, 87, 93, 99, 119, 126, 133, 156, 164, 172, 198, 207, 216, 245, 255, 265, 297, 308, 319, 354, 366, 378, 416, 429, 442, 483, 497, 511, 555, 570, 585, 632, 648, 664, 714, 731, 748, 801, 819
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OFFSET
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0,4
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COMMENTS
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For a guide to related sequences, see A211422.
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LINKS
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FORMULA
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a(n) = a(n-1) + 2*a(n-3) - 2*a(n-4) - a(n-6) + a(n-7).
G.f.: x^3*(2 + x + x^2 + x^3) / ((1 - x)^3*(1 + x + x^2)^2). - Colin Barker, Dec 03 2017
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MATHEMATICA
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t[n_] := t[n] = Flatten[Table[w - 3 x + 3 y, {w, 1, n}, {x, 1, n}, {y, 1, n}]]
c[n_] := Count[t[n], 0]
t = Table[c[n], {n, 0, 70}] (* A211546 *)
FindLinearRecurrence[t]
LinearRecurrence[{1, 0, 2, -2, 0, -1, 1}, {0, 0, 0, 2, 3, 4, 9}, 56] (* Ray Chandler, Aug 02 2015 *)
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PROG
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(PARI) concat(vector(3), Vec(x^3*(2 + x + x^2 + x^3) / ((1 - x)^3*(1 + x + x^2)^2) + O(x^40))) \\ Colin Barker, Dec 03 2017
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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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