

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
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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. A137815A137818.
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



