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A086368
Nonsquarefree numbers k such that sigma(k) is squarefree.
1
4, 8, 9, 16, 18, 20, 25, 36, 45, 49, 50, 64, 72, 80, 100, 104, 116, 117, 121, 128, 144, 148, 169, 180, 196, 200, 208, 225, 234, 242, 244, 256, 261, 289, 292, 296, 320, 325, 333, 361, 369, 404, 436, 441, 450, 452, 464, 488, 512, 529, 548, 549, 576, 578, 584, 592
OFFSET
1,1
LINKS
EXAMPLE
k = 45 = 3*3*5 and sigma(45) = 78 = 2*3*13.
MAPLE
filter:= n -> not numtheory:-issqrfree(n) and numtheory:-issqrfree(numtheory:-sigma(n)):
select(filter, [$1..1000]); # Robert Israel, May 11 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 05 2003
STATUS
approved