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A239578
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Smallest number m such that the numerator of sigma(m)/m is equal to n, or zero if no such m exists.
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3
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1, 6, 2, 3, 24, 5, 4, 7, 10, 1080, 35640, 11, 9, 13, 8, 33, 297600, 17, 588, 19, 20, 1782, 1907020800, 23, 216, 45, 34, 78
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OFFSET
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1,2
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COMMENTS
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If n-1 is prime, a(n) = n-1.
a(29) <= 1176249221876579007725568000.
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LINKS
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EXAMPLE
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a(2) = 6 since 6 is the first perfect number, with 2 as the numerator of sigma(6)/6.
a(3) = 2 because sigma(2)/2 = 3/2 and it is the first number that gives this numerator.
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PROG
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(PARI) a(n) = {k = 1; while (numerator(sigma(k)/k) != n, k++); k; }
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CROSSREFS
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Cf. A017665 (numerator of sigma(n)/n), A162657 (similar sequence but related to denominators).
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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