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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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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| 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
| Donovan Johnson, Table of n, a(n) for n = 1..100
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PROG
| (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
| Cf. A137815-A137818.
Sequence in context: A017658 A043650 A140861 * A145537 A183735 A147525
Adjacent sequences: A137816 A137817 A137818 * A137820 A137821 A137822
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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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EXTENSIONS
| More terms from Russell Pochis (joebobpumpkin(AT)gmail.com), May 30 2010
Typo in data corrected by D. S. McNeil, Aug 17 2010
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