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A075768
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A Wallis pair (x,y) satisfies sigma(x^2) = sigma(y^2); sequence gives x's for indecomposable Wallis pairs with x < y (ordered by values of x).
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4
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4, 326, 406, 627, 740, 880, 888, 1026, 1110, 1284, 1510, 1528, 2013, 2072, 3216, 3260, 3912, 4866, 4946, 5064, 5064, 5829, 7248, 9768, 10536, 10686, 11836, 12122, 13066, 13398, 13986, 14248, 14397, 15000, 15000, 15430, 15504, 15544, 15544
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| If (x,y) and (u,v) are Wallis pairs, a is from (x,y) and c is from (u,v) and gcd(a,c)=1, b is from (x,y) and d is from(u,v) and gcd(b,d)=1, then (ac,bd) is also a Wallis pair. Such pairs are called decomposable. If (x,y) and (cx,cy) are Wallis pairs then (cx,cy) is also called decomposable.
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REFERENCES
| I. Kaplansky, The challenges of Fermat, Wallis and Ozanam (and several related challenges): II. Fermat's second challenge, Preprint, 2002.
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EXAMPLE
| (4,5) is a Wallis pair since sigma(16) = sigma(25) = 31.
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CROSSREFS
| Cf. A075769, A072182, A072186, A077053.
Sequence in context: A053917 A005832 A195501 * A135442 A086895 A173367
Adjacent sequences: A075765 A075766 A075767 * A075769 A075770 A075771
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KEYWORD
| nonn,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Oct 13 2002
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EXTENSIONS
| Corrected and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Oct 22 2002
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