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Search: id:A136410
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| A136410 |
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Numbers n having a proper divisor d > 2 such that d-1 divides n-1. |
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+0
1
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| 9, 15, 16, 21, 25, 27, 28, 33, 36, 39, 40, 45, 49, 51, 52, 57, 63, 64, 65, 66, 69, 75, 76, 81, 85, 87, 88, 91, 93, 96, 99, 100, 105, 111, 112, 117, 120, 121, 123, 124, 125, 126, 129, 133, 135, 136, 141, 144, 145, 147, 148
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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E.g. consider n=91: we can take d=7, 7 divides 91 and 6 divides 90, so 91 is in the sequence.
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MATHEMATICA
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fQ[n_] := Block[{d = Select[ Take[ Divisors@ n, {2, -2}], # > 2 &]}, Union[IntegerQ /@ ((n - 1)/(d - 1))][[ -1]]]; Select[ Range@ 175, !PrimeQ@ # && fQ@ # &] (* Robert G. Wilson v, (rgwv(AT)rgwv.com), May 04 2008 *)
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CROSSREFS
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Sequence in context: A130119 A058957 A105882 this_sequence A066942 A061838 A037002
Adjacent sequences: A136407 A136408 A136409 this_sequence A136411 A136412 A136413
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KEYWORD
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nonn
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AUTHOR
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J. Perry (johnandruth(AT)jrperry.orangehome.co.uk), Apr 13 2008
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EXTENSIONS
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Definition, terms and offset corrected by M. F. Hasler (www.univ-ag.fr/~mhasler), May 01 2008
Edited by N. J. A. Sloane (njas(AT)research.att.com), May 10 2008
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