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Search: id:A137817
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| A137817 |
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Cubeful "year numbers" (such that phi(n) = 2 phi(sigma(n)): A137815). |
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+0
3
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| 295569, 295947, 1586763, 1811079, 1964375, 2069469, 4473387, 5854375, 6820555, 7285923, 10936053, 12233457, 13260625, 18029709, 18052767, 21153663, 21576537, 21604131, 22182093, 22877451, 23744043, 25536875, 28340307, 34102775
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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See A137815 for general comments and references about "year numbers". This is the subsequence of cubeful elements of A137815, i.e. its intersection with A046099. As such, it is of course also a subsequence of A137816.
There are only 56 such numbers below 10^8.
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LINKS
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M. F. Hasler, Table of n, a(n) for n=1,...,56.
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PROGRAM
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(PARI) for( i=1, #A137816, vecmax( factor( A137816[i] )[, 2])>2 && print1(A137816[i]", "))
(PARI) for( i=1, #A046099, eulerphi(A046099[i])==2*eulerphi(sigma(A046099[i])) && print1( A046099[i] ", "))
(PARI) for( n=1, 10^9, issquarefree(n) && next; vecmax(factor(n)[, 2])>2 || next; eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", "))
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CROSSREFS
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Cf. A137815-A137819, A006872. A046099. A067704.
Sequence in context: A050249 A023351 A109031 this_sequence A137818 A164946 A048906
Adjacent sequences: A137814 A137815 A137816 this_sequence A137818 A137819 A137820
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KEYWORD
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nonn
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AUTHOR
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Richard K. Guy (rkg(AT)cpsc.ucalgary.ca), Richard J. Mathar (mathar(AT)strw.leidenuniv.nl) and M. F. Hasler (MHasler(AT)univ-ag.fr), Feb 11 2008
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