The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 13 21:24 EDT 2021. Contains 342941 sequences. (Running on oeis4.)