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Search: id:A135470
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| A135470 |
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Composite numbers n that divide 2 * sigma(n) - d(n) [that is, 2 * sum of divisors - number of divisors]. |
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+0
1
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| 18, 70, 88, 132, 780, 11096, 17816, 518656, 1713592, 9928792, 11547352, 13499120, 17999992, 89283592, 134094848, 173482552, 175519344, 318836720, 903230984, 1081850752, 2146926592, 16709332608, 18543186000, 34177937500
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OFFSET
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1,1
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COMMENT
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It is conjectured that there are no odd terms and that the sequence is infinite.
3*10^11 < a(25) <= 2251798907715584. [From Donovan Johnson (donovan.johnson(AT)yahoo.com), Oct 13 2008]
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LINKS
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Yong-Gao Chen and Jin-Hui Fang, On n phi(n)d(n) + 2 and n phi(n) sigma(n)+1, INTEGERS: Electronic J. Combinatorial Number Theory: 8 (2008), #A7.
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CROSSREFS
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Sequence in context: A063523 A045234 A158056 this_sequence A059224 A088490 A069058
Adjacent sequences: A135467 A135468 A135469 this_sequence A135471 A135472 A135473
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KEYWORD
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nonn
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AUTHOR
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Richard Guy (rkg(AT)cpsc.ucalgary.ca), Feb 08 2008
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EXTENSIONS
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Corrected by Emeric Deutsch, Feb 29 2008
a(15)-a(24) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Oct 13 2008
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