The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A237043

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A237043

Numbers n such that 2^n - 1 is not squarefree, but 2^d - 1 is squarefree for every proper divisor d of n.
(history; published version)

#44 by Bruno Berselli at Sun Jul 28 02:22:56 EDT 2019

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reviewed

approved

#43 by Sean A. Irvine at Sat Jul 27 23:34:25 EDT 2019

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proposed

reviewed

#42 by Michael De Vlieger at Sun Jul 07 16:07:11 EDT 2019

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editing

proposed

#41 by Michael De Vlieger at Sun Jul 07 16:07:09 EDT 2019

MATHEMATICA

Select[Range@ 160, And[AllTrue[2^#2 - 1, SquareFreeQ], ! SquareFreeQ[2^First@ #1 - 1]] & @@ TakeDrop[Divisors@ #, -1] &] (* Michael De Vlieger, Jul 07 2019 *)

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proposed

editing

#40 by Michel Marcus at Wed Jul 03 06:27:23 EDT 2019

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editing

proposed

#39 by Michel Marcus at Wed Jul 03 06:27:19 EDT 2019

COMMENTS

Comment from _From _Daniel Suteu_, Jul 03 2019: (Start)

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proposed

editing

#38 by Daniel Suteu at Wed Jul 03 06:21:33 EDT 2019

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editing

proposed

#37 by Daniel Suteu at Wed Jul 03 06:18:30 EDT 2019

COMMENTS

a(15) >= 1207. - Max Alekseyev, Sep 28 2015

Comment from Daniel Suteu, Jul 03 2019: (Start)

The following numbers are also in the sequence: {1755, 2265, 2485, 2756, 3081, 3164, 4112, 6757, 8251, 13861, 18533}.

Probably, the following numbers are also terms: {3422, 5253, 6806, 8164, 9316, 11342, 12550, 15025, 15026, 17030, 17404, 17468, 18145, 19670, 19701, 22052}. (End)

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approved

editing

#36 by N. J. A. Sloane at Thu Feb 23 22:17:05 EST 2017

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proposed

approved

#35 by Robert Price at Thu Feb 23 18:11:13 EST 2017

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editing

proposed