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A060735
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Where n / (phi(n) + 1) increases.
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17
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1, 2, 4, 6, 12, 18, 24, 30, 60, 90, 120, 150, 180, 210, 420, 630, 840, 1050, 1260, 1470, 1680, 1890, 2100, 2310, 4620, 6930, 9240, 11550, 13860, 16170, 18480, 20790, 23100, 25410, 27720, 30030, 60060, 90090, 120120, 150150, 180180, 210210
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OFFSET
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1,2
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COMMENTS
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Except for the initial 1, this sequence is a primorial (A002110) followed by its multiples until the next primorial, then the multiples of that primorial and so on. - Wilfredo Lopez (chakotay147138274(AT)yahoo.com), Dec 28 2006
a(1)=1, a(2)=2. For n >=3, a(n) = the smallest integer that both is > a(n-1) and is divisible by every prime that LCM(a(1),a(2),a(3),...a(n)) is divisible by. [From Leroy Quet, Feb 23 2010]
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LINKS
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Enrique Pérez Herrero, Table of n, a(n) for n = 1..5000
Michel Planat, Riemann hypothesis from the Dedekind psi function, arXiv:1010.3239v2.
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FORMULA
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a(1) = 1, a(n) = a(n-1) + sfk(a(n-1)) with sfk=A007947, squarefree kernel. - Reinhard Zumkeller, Apr 10 2006
a(A101301(n)+1)=A002110(n). - Enrique Pérez Herrero, Jun 10 2012
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MAPLE
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seq(seq(k*mul(ithprime(i), i=1..n-1), k=1..ithprime(n)-1), n=1..10); (from Vladeta Jovovic, Apr 08 2004)
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MATHEMATICA
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a = 0; Do[ b = n/(EulerPhi[ n ] + 1); If[ b > a, a = b; Print[ n ] ], {n, 1, 10^6} ]
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CROSSREFS
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Cf. A000010, A055719.
Cf. A002110.
Sequence in context: A072121 A175305 A171923 * A181416 A225566 A051683
Adjacent sequences: A060732 A060733 A060734 * A060736 A060737 A060738
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KEYWORD
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nonn,changed
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AUTHOR
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Robert G. Wilson v, Apr 23 2001
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EXTENSIONS
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Definition corrected by Franklin T. Adams-Watters, Apr 16 2009
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STATUS
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approved
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