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Search: id:A137819
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| A137819 |
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Year numbers, i.e. phi(n) = 2 phi(sigma(n)), divisible by a 5th prime power. |
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+0
5
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OFFSET
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1,1
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COMMENT
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See A137815 for more comments and references about "year numbers". This is the subsequence of elements of A137815 divisible by a 5th prime power. As such, it is of course also a subsequence of A137818 (those divisible by a 4th prime power).
There are only 5 such numbers below 10^8.
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PROGRAM
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(PARI) for( i=1, #A137816, vecmax(factor(A137816[i])[, 2])>4 & print1(A137816[i])", ")
(PARI) for( n=1, 10^9, issquarefree(n) && next; vecmax(factor(n)[, 2])>4 || next; eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", "))
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CROSSREFS
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Cf. A137815-A137818.
Adjacent sequences: A137816 A137817 A137818 this_sequence A137820 A137821 A137822
Sequence in context: A017394 A017658 A043650 this_sequence A115495 A015347 A064820
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KEYWORD
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more,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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