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A070237
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Numbers n such that the sign of core(n)-phi(n) is not equal to 2*mu(n)^2-1, where core(x) is the squarefree part of x.
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1
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1, 420, 660, 780, 840, 1320, 1560, 4620, 5460, 7140, 7980, 8580, 9240, 9660, 10920, 11220, 12012, 12180, 12540, 13020, 13260, 14280, 14820, 15180, 15540, 15708, 15960, 17160, 17220, 17556, 17940, 18060, 18564, 19140, 19320, 19380, 19740
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Terms seem always congruent to 3. For almost k, sign(core(k)-phi(k))=2*mu(k)^2-1=2*A008683(k)-1.
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FORMULA
| a(n)=C*n + O(n), with C a constant conjectured to be a(2) = 420.
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PROG
| (PARI) for(n=1, 25000, if(abs(sign(core(n)-eulerphi(n)-2*moebius(n)^2+1)>0, print1(n, ", ")))
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CROSSREFS
| See A013929 for another interpretation.
Sequence in context: A024410 A200521 A189982 * A156687 A191934 A147775
Adjacent sequences: A070234 A070235 A070236 * A070238 A070239 A070240
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KEYWORD
| easy,nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), May 08 2002
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