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Search: id:A069819
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| A069819 |
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Numbers n such that 1/(sum(p|n,1/p)-1), where p are the prime divisors of n, is an integer. |
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+0
2
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| 30, 60, 90, 120, 150, 180, 240, 270, 300, 360, 450, 480, 540, 600, 720, 750, 810, 858, 900, 960, 1080, 1200, 1350, 1440, 1500, 1620, 1716, 1722, 1800, 1920, 2160, 2250, 2400, 2430, 2574, 2700, 2880, 3000, 3240, 3432, 3444, 3600, 3750, 3840, 4050, 4320
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OFFSET
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1,1
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COMMENT
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Sequence is generated by A007850(n). For example: 30,858,1722 (30=2*3*5, 858=2*3*11*13, 1722=2*3*11*13) generate numbers of the form 2^a*3^b*5^c, 2^a*3^b*7^c*41^d, 2^a*3^b*11^c*13^d, (a,b,c,d => 1), which are in the sequence.
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EXAMPLE
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E.g. if n=30=2*3*5 1/(sum(p|n,1/p)-1)=1/(1/2+1/3+1/5-1)=30 hence 30 is in the sequence.
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CROSSREFS
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Sequence in context: A074915 A056954 A050519 this_sequence A108454 A064783 A053014
Adjacent sequences: A069816 A069817 A069818 this_sequence A069820 A069821 A069822
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 28 2002
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