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A307222
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Deficient numbers k at least one of whose divisors is the sum of other distinct divisors of k.
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0
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45, 63, 99, 105, 110, 117, 130, 135, 154, 165, 170, 182, 189, 195, 225, 231, 238, 255, 266, 273, 285, 286, 297, 315, 322, 345, 351, 357, 374, 385, 399, 405, 418, 429, 441, 455, 459, 475, 483, 494, 495, 506, 513, 525, 561, 567, 585, 595, 598, 609, 621, 627, 646
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OFFSET
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1,1
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COMMENTS
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Erdős used the term "integers with the property P" for numbers k such that all the 2^d(k) sums formed from the d(k) divisors of k are distinct and proved that they are all deficient numbers and have a positive density. This sequence lists deficient numbers not having this property.
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LINKS
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EXAMPLE
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45 is in this sequence since its divisors are 1, 3, 5, 9, 15, 45 whose sum is 78 < 90, and thus it is deficient, yet the divisor 15 is the sum of other divisors of 45: 1 + 5 + 9.
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MATHEMATICA
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T[n_, k_] := Module[{d = Divisors[n]}, SeriesCoefficient[Series[Product[1 + x^d[[i]], {i, Length[d]}], {x, 0, k}], k]]; seqQ[n_] := DivisorSigma[1, n] < 2n && Max[T[n, #] & /@ Range[DivisorSigma[1, n]]] > 1; Select[Range[1000], seqQ]
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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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