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Search: id:A072188
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| A072188 |
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Numbers n such that n divides sigma(n-1)+sigma(n)+sigma(n+1), where sigma() is the "sum of integer divisors" function. |
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1
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| 2, 5, 7, 33, 18336, 19262, 38184, 54722, 458010, 1402224, 1473624, 1708480, 3680560, 3733584, 5829841, 7769904, 13204262
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Heuristics would seem to indicate that this sequence is infinite and sparse. Compare this sequence to the natural numbers n such that n divides sigma(n) - the perfect and multiperfect numbers.
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EXAMPLE
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33 is in this list because sigma(32)+sigma(33)+sigma(34)=63+48+54=165=33*5
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PROGRAM
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(PARI) for(i=2, 99999, if((sigma(i-1)+sigma(i)+sigma(i+1))%i==0, print(i)))
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CROSSREFS
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Cf. A007691.
Sequence in context: A042931 A085394 A041875 this_sequence A028432 A019409 A123232
Adjacent sequences: A072185 A072186 A072187 this_sequence A072189 A072190 A072191
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KEYWORD
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nonn
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AUTHOR
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Jack Brennen (jb(AT)brennen.net), Jul 01 2002
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EXTENSIONS
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More terms from Jason Earls (zevi_35711(AT)yahoo.com), Aug 25 2002
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