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A055153
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Numbers n such that sigma(n) = 7n/2.
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6
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4320, 4680, 26208, 20427264, 197064960, 21857648640, 57575890944, 88898072401645056, 301183421949935616, 9083288595228991885541376, 22290964134962716779872256, 230361837156847526055247872
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Comment from Yasutoshi Kohmoto (zbi74583(AT)boat.zero.ad.jp), May 10 2008: This sequence also contains the term 230361837156847526055247872.
Comment from Avinoam Kalma (a.kalma(AT)gmail.com), May 04 2009: 301183421949935616 also belongs to this sequence.
22290964134962716779872256 is in this sequence. [From Gerard P. Michon (g.michon(AT)att.net), May 10 2009]
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LINKS
| G. P. Michon, Table of n, a(n) for n=1..21
Walter Nissen, Abundancy : Some Resources
Walter Nissen, Home Page (listed in lieu of email address)
Walter Nissen, Abundancy : Some Resources
Walter Nissen, Primitive Friendly Pairs with friends < 2^34 with denom < 20000
G.P. Michon, Multiperfect and hemiperfect numbers [From Gerard P. Michon (g.michon(AT)att.net), Jun 04 2009]
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EXAMPLE
| Sigma(4320)=15120=7*4320/2, so 4320 is in the sequence.
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MAPLE
| with(numtheory); P:=proc(i) local n; for n from 1 by 1 to i do if sigma(n)/n=7/2 then; print(n); fi; od; end: P(100000000) [From Paolo P. Lava (paoloplava(AT)gmail.com), Sep 18 2008]
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MATHEMATICA
| Do[If[DivisorSigma[1, m]==3.5*m, Print[m]], {m, 2*10^8}]
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CROSSREFS
| Cf. A007539, A000396, A005820, A027687, A000203.
Cf. A141643, A141645.
Sequence in context: A124596 A165067 A190929 * A190011 A145312 A008409
Adjacent sequences: A055150 A055151 A055152 * A055154 A055155 A055156
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KEYWORD
| nonn
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AUTHOR
| Jud McCranie (JudMcCranie(AT)ugaalum.uga.edu), Jun 16 2000
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EXTENSIONS
| Terms confirmed through a(5) by Ray Chandler (rayjchandler(AT)sbcglobal.net), Sep 18 2008
a(6) and a(7) found by Yasutoshi Kohmoto and confirmed by W. Bomfim (webonfim(AT)bol.com.br), Oct 19 2008
Edited by N. J. A. Sloane (njas(AT)research.att.com), Sep 19 2008, Apr 18 2009
a(8), a(10), a(12) [and above] found by Michel Marcus, added by Gerard P. Michon (g.michon(AT)att.net), Jun 04 2009
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