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A349675
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a(n) is the number of attainable partitions of n.
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0
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1, 1, 2, 2, 3, 3, 5, 5, 7, 7, 9, 9, 13, 13, 17, 17, 21, 21, 27, 27, 34, 34, 41, 41, 51, 51, 62, 62, 73, 73, 88, 88, 105, 105, 122, 122, 144, 144, 168, 168, 193, 193, 225, 225, 260, 260, 296, 296, 340, 340, 388, 388, 438, 438, 498, 498, 564, 564, 632, 632, 713, 713
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OFFSET
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0,3
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COMMENTS
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An attainable partition p of n is a partition such that, when written so that p_1 >= p_2 >= ... >= p_r, we have Sum_{i=1..r} (3-2*i)*p_i >= 0.
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LINKS
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FORMULA
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G.f.: (1/(1-x))*Product_{i>=1} 1/(1-x^(i*(i+1)). See Theorem 1.1 p. 1.
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MATHEMATICA
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nterms=50; Table[Total[Map[If[Sum[(3-2i)#[[i]], {i, Length[#]}]>=0, 1, 0]&, IntegerPartitions[n]]], {n, 0, nterms-1}] (* Paolo Xausa, Nov 24 2021 *)
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PROG
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(PARI) a(n) = my(nb=0); forpart(p=n, p = vecsort(p, , 4); if (sum(i=1, #p, (3-2*i)*p[i]) >= 0, nb++); ); nb;
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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