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Search: id:A140525
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| A140525 |
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a(1)=2. For n >=2, a(n) = the least integer >= a(n-1) that is not coprime to both a(n-1)+1 and a(n-1). |
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2
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| 2, 6, 14, 18, 38, 42, 86, 90, 98, 102, 206, 210, 422, 426, 434, 438, 878, 882, 1766, 1770, 1778, 1782, 3566, 3570, 7142, 7146, 7154, 7158, 14318, 14322, 28646, 28650, 28658, 28662, 57326, 57330, 114662, 114666, 114674, 114678, 229358, 229362, 229400
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Also: a(n+1) = a(n)+1 + least prime factor of (a(n)+1), according to an observation by Peter Pein, proved by M. F. Hasler, cf. link. [From M. F. Hasler (MHasler(AT)univ-ag.fr), Feb 09 2009]
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LINKS
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Peter Pein and M. F. Hasler: Post to the SeqFan list, Feb 09 2009 [From M. F. Hasler (MHasler(AT)univ-ag.fr), Feb 09 2009]
Leroy Quet, Home Page (listed in lieu of email address)
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MATHEMATICA
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a = {2}; Do[ i = a[ [ -1 ] ] + 1; While[ Min[ GCD[ a[ [ -1 ] ], i ], GCD[ a[ [ -1 ] ] + 1, i ] ] == 1, i++ ]; AppendTo[ a, i ], {40} ]; a [ From Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Aug 04 2008 ]
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PROGRAM
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(PARI) print1(a=2); for(i=2, 99, print1(", "a+=1+factor(a+1)[1, 1])) [From M. F. Hasler (MHasler(AT)univ-ag.fr), Feb 09 2009]
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CROSSREFS
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Equals A144751 - 1.
Sequence in context: A057214 A139269 A163777 this_sequence A032643 A067664 A130800
Adjacent sequences: A140522 A140523 A140524 this_sequence A140526 A140527 A140528
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet Jul 02 2008
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EXTENSIONS
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More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Aug 04 2008
a(42)-a(43) from Ray Chandler (rayjchandler(AT)sbcglobal.net), Jun 25 2009
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