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Search: id:A111934
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| A111934 |
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Denominator of f(n) := Product_{i=1..n} sigma(i)/i. |
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+0
2
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| 1, 2, 1, 2, 5, 5, 5, 1, 1, 5, 55, 55, 55, 55, 275, 275, 4675, 4675, 17765, 88825, 88825, 977075, 22472725, 4494545, 112363625, 112363625, 22472725, 22472725, 130341805, 651709025, 651709025, 651709025, 7168799275, 121869587675, 609347938375, 609347938375
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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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
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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
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with(numtheory); f:=n->mul(sigma(i)/i, i=1..n);
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MATHEMATICA
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f[n_] := Denominator@ Product[ DivisorSigma[1, i]/i, {i, n}]; Array[f, 36] (from Robert G. Wilson v (rgwv(at)rgwv.com), May 01 2006)
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CROSSREFS
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Cf. A111928.
Sequence in context: A167482 A137327 A143913 this_sequence A098509 A019910 A084309
Adjacent sequences: A111931 A111932 A111933 this_sequence A111935 A111936 A111937
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KEYWORD
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nonn,frac
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Nov 27 2005
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