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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1811079, 4473387, 67009923, 77242167, 88605819, 110475819, 120781449, 132208767, 134082297, 165515319, 183408867, 225548469, 232275681, 272876607, 284339403, 326557251, 349538247, 402371793, 425844621, 501668883, 566867727
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OFFSET
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1,1
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COMMENTS
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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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LINKS
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PROG
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(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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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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More terms from Russell Pochis (joebobpumpkin(AT)gmail.com), May 30 2010
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STATUS
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approved
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