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A172516
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Least number k such that sigma(k) >= 2^n.
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1
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2, 3, 6, 10, 18, 30, 60, 108, 180, 360, 720, 1260, 2520, 5040, 9240, 17640, 35280, 65520, 131040, 257040, 498960, 982800, 1884960, 3603600, 7207200, 14414400, 28274400, 56548800, 110270160, 220540320, 428828400, 845404560, 1690809120
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OFFSET
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1,1
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COMMENTS
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For n-bit arithmetic, m=a(n)-1 is the largest number for which sigma(m) can be computed without overflow. This is a subsequence of the highly abundant numbers, A002093, which is very useful for computing this sequence. a(63) is 1454751268447276800.
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LINKS
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FORMULA
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a(n) <= 2 * a(n-1)
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MATHEMATICA
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k=1; Table[While[DivisorSigma[1, k]<2^n, k++ ]; k, {n, 20}]
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CROSSREFS
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A141847 (least number k such that sigma2(k) >= 2^n)
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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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