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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 25 21:41 EDT 2017. Contains 287059 sequences.