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A307112
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Primitive 3-abundant numbers: Numbers k such that sigma(k) > 3k (A068403) all of whose proper divisors d are 3-deficient numbers having sigma(d) < 3d.
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4
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180, 420, 504, 660, 780, 1584, 1848, 1872, 1890, 2184, 2352, 2376, 2772, 2856, 3150, 3192, 3276, 4284, 4410, 4788, 4896, 5100, 5292, 5700, 5796, 6864, 6900, 6930, 7344, 7728, 8190, 8208, 8424, 9744, 10296, 10416, 10710, 10944, 11550, 11970, 12012, 12432, 12870
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OFFSET
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1,1
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COMMENTS
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Analogous to A071395 with abundancy index 3 instead of 2.
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REFERENCES
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Paul Erdős and János Surányi, Topics in the Theory of Numbers, New York: Springer, 2003, p. 243.
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LINKS
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MATHEMATICA
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Select[Range@50000, DivisorSigma[1, #] > 3 # && Times @@ Boole@ Map[DivisorSigma[1, #] < 3 # &, Most@ Divisors@ #] == 1 &] (* after Michael De Vlieger at A071395 *)
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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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