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A111928
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Numerator of f(n) := Product_{i=1..n} sigma(i)/i.
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1
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1, 3, 2, 7, 21, 42, 48, 18, 26, 234, 2808, 6552, 7056, 12096, 96768, 187488, 3374784, 7312032, 29248128, 307105344, 467970048, 8423460864, 202163060736, 101081530368, 3133527441408, 5061852020736, 1499808006144, 2999616012288, 17997696073728, 215972352884736
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| R. K. Guy observes (Nov 23, 2005) that it appears that f(n) is an integer iff n = 1, 3, 8, 9, when f(n) = 1, 2, 18, 26 respectively.
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EXAMPLE
| 1, 3/2, 2, 7/2, 21/5, 42/5, 48/5, 18, 26, 234/5, 2808/55, 6552/55, 7056/55, 12096/55, 96768/275, 187488/275, 3374784/4675, 7312032/4675, 29248128/17765, 307105344/88825, ...
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MAPLE
| with(numtheory); f:=n->mul(sigma(i)/i, i=1..n);
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MATHEMATICA
| f[n_] := Numerator@ Product[ DivisorSigma[1, i]/i, {i, n}]; Array[f, 30] (from Robert G. Wilson v (rgwv(at)rgwv.com), May 01 2006)
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CROSSREFS
| Cf. A111934.
Sequence in context: A177115 A196537 A173099 * A100985 A176802 A021757
Adjacent sequences: A111925 A111926 A111927 * A111929 A111930 A111931
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KEYWORD
| nonn,frac
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Nov 27 2005
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