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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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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; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| 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
| M. F. Hasler, Table of n, a(n) for n=1,...,56.
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PROG
| (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
| Cf. A137815-A137819, A006872. A046099. A067704.
Sequence in context: A206237 A023351 A109031 * A137818 A164946 A204318
Adjacent sequences: A137814 A137815 A137816 * A137818 A137819 A137820
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KEYWORD
| nonn
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AUTHOR
| Richard K. Guy (rkg(AT)cpsc.ucalgary.ca), Richard J. Mathar (mathar(AT)strw.leidenuniv.nl) and M. F. Hasler (www.univ-ag.fr/~mhasler), Feb 11 2008
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