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A137816
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Non-squarefree "year numbers" (numbers n such that phi(n) = 2 phi(sigma(n)): A137815).
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6
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5491, 8075, 25317, 27455, 71383, 72283, 76131, 104975, 138575, 193041, 203167, 295569, 295947, 298775, 334951, 356915, 361415, 400843, 451535, 492275, 509575, 572975, 589475, 595975, 654493, 683757, 815975, 862087, 876627, 919075, 936729
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OFFSET
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1,1
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COMMENTS
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This is the subsequence of non-squarefree elements of A137815. See there for more comments and references.
There are only 32 such numbers below 10^6, 145 below 10^7 and 785 below 10^8.
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LINKS
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M. F. Hasler, Table of n, a(n) for n=1,...,785.
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PROG
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(PARI) { for( n=1, 10^8, !issquarefree(n) && eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", "))
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CROSSREFS
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Cf. A137815-A137819, A006872, A067704.
Sequence in context: A031572 A045108 A203791 * A138760 A031617 A045132
Adjacent sequences: A137813 A137814 A137815 * A137817 A137818 A137819
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KEYWORD
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nonn
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AUTHOR
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Richard K Guy, R. J. Mathar and M. F. Hasler, Feb 11 2008
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STATUS
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approved
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