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A078560
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Denominator of product_{i=1}^n (p_i+1)/(p_i-1). Numerators are in A078559.
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1
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1, 1, 1, 1, 5, 5, 10, 1, 11, 11, 11, 11, 55, 5, 115, 1495, 8671, 43355, 476905, 16691675, 16691675, 43398355, 254190365, 559218803, 559218803, 13980470075, 1075420775, 56997301075, 1036314565, 1036314565, 1036314565, 6123676975
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,5
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COMMENTS
| a(n)=A005867(n)/A078558(n)
According to Koninck (2009), a(8) is the largest value of this sequence known to be 1 (meaning that the product is an integer). [From Alonso del Arte, Aug 23 2011]
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REFERENCES
| R. K. Guy, Unsolved Problems in Number Theory, B48.
J.-M. De Koninck, Those Fascinating Numbers, Amer. Math. Soc., 2009, page 6.
F. Smarandache, "Only Problems, not Solutions!", Xiquan Publ., Phoenix-Chicago, 1993
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LINKS
| F. Smarandache, Only Problems, Not Solutions!.
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MATHEMATICA
| Denominator[Table[Product[(Prime[i] + 1)/(Prime[i] - 1), {i, n}], {n, 30}]] (* From Alonso del Arte, Aug 23 2011 *)
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CROSSREFS
| Cf. A000203, A002110, A000005, A005867, A054640, A020492, A078558, A078559.
Sequence in context: A173322 A097910 A049122 * A040021 A003882 A168284
Adjacent sequences: A078557 A078558 A078559 * A078561 A078562 A078563
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KEYWORD
| nonn,frac
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Dec 06 2002
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EXTENSIONS
| Improved definition from Frank Adams-Watters (FrankTAW(AT)Netscape.net), Dec 02 2005
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