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A280296 Squarefree numbers k such that 2^k - 1 is divisible by a square > 1. 5
6, 21, 30, 42, 66, 78, 102, 105, 110, 114, 138, 155, 174, 186, 210, 222, 231, 246, 253, 258, 273, 282, 310, 318, 330, 354, 357, 366, 390, 399, 402, 426, 438, 462, 465, 474, 483, 498, 506, 510, 534, 546, 570, 582, 602, 606, 609, 618, 642, 651, 654, 678, 690, 714, 759, 762, 770, 777, 786, 798, 822 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Intersection of A049094 and A005117. - Michel Marcus, Dec 31 2016
LINKS
EXAMPLE
6 is in this sequence because 2^6 - 1 = 63 is divisible by 9 = 3^2.
PROG
(Magma) [n: n in [1..200] | IsSquarefree(n) and not IsSquarefree(2^n-1)];
CROSSREFS
Sequence in context: A034897 A347875 A287165 * A325407 A239920 A173622
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(38)=498 inserted by Amiram Eldar, Oct 23 2019
STATUS
approved

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Last modified June 14 05:27 EDT 2024. Contains 373393 sequences. (Running on oeis4.)