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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

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

Cf. A065303, A087249, A065301.

Sequence in context: A140612 A225353 A034023 * A034024 A299117 A339462

Adjacent sequences:  A086365 A086366 A086367 * A086369 A086370 A086371

KEYWORD

nonn

AUTHOR

Labos Elemer, Sep 05 2003

STATUS

approved

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Last modified May 14 18:23 EDT 2021. Contains 343900 sequences. (Running on oeis4.)