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 A137819 Year numbers, i.e., phi(n) = 2 phi(sigma(n)), divisible by a 5th prime power. 5
 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; text; internal format)
 OFFSET 1,1 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. LINKS Donovan Johnson, Table of n, a(n) for n = 1..100 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", ")) CROSSREFS Cf. A137815-A137818. Sequence in context: A140861 A234866 A249196 * A145537 A183735 A147525 Adjacent sequences:  A137816 A137817 A137818 * A137820 A137821 A137822 KEYWORD nonn AUTHOR R. K. Guy, R. J. Mathar and M. F. Hasler, Feb 11 2008 EXTENSIONS More terms from Russell Pochis (joebobpumpkin(AT)gmail.com), May 30 2010 Typo in data corrected by D. S. McNeil, Aug 17 2010 STATUS approved

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Last modified May 11 00:21 EDT 2021. Contains 343784 sequences. (Running on oeis4.)