The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A230626

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A230626

Iterate the map x -> A230625(x) starting at n; sequence gives number of steps to reach a prime, or -1 if no prime is ever reached.
(history; published version)

#76 by Susanna Cuyler at Mon Mar 16 19:01:55 EDT 2020

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proposed

approved

#75 by Robert Price at Mon Mar 16 15:14:04 EDT 2020

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editing

proposed

#74 by Robert Price at Mon Mar 16 15:13:53 EDT 2020

MATHEMATICA

fn[n_] := FromDigits[Flatten[IntegerDigits[ReplaceAll[FactorInteger[n], {x_, 1} -> {x}], 2]], 2];

Map[Length, Table[NestWhileList[fn, n, # != 1 && ! PrimeQ[#] &], {n, 2, 40}], {1}] - 1 (* Robert Price, Mar 16 2020 *)

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approved

editing

#73 by Alois P. Heinz at Fri Feb 15 12:01:18 EST 2019

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reviewed

approved

#72 by Michel Marcus at Fri Feb 15 11:52:57 EST 2019

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proposed

reviewed

#71 by Georg Fischer at Fri Feb 15 11:35:57 EST 2019

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editing

proposed

#70 by Georg Fischer at Fri Feb 15 11:35:53 EST 2019

KEYWORD

nonn,sign,base

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approved

editing

#69 by N. J. A. Sloane at Tue Jun 20 23:34:41 EDT 2017

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editing

approved

#68 by N. J. A. Sloane at Tue Jun 20 23:34:39 EDT 2017

COMMENTS

a(217) = a(255) = a(446) = a(558) = a(717) = a(735) = a(775) = a(945) = a(958) = -1 since the trajectory either converges to (1007,1269) or to (1503,3751). For 3932, a possibly infinite trajectory emerges. 255987 has several preimages, e.g. a(7^25*31^19) = a(3^28*7^7*19) = a(7^12*31^51) = -1. a(3568) = 74 ending in the prime 318792605899852268194734519209581. - Chai Wah Wu, Jun 16 2017

See A288894 for the trajectory of 3932. - Sean A. Irvine, Jun 18 2017

CROSSREFS

Cf. A230625, A230627, A080670, A287875, A287878, A288847, A288894.

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approved

editing

#67 by Joerg Arndt at Mon Jun 19 08:08:27 EDT 2017

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reviewed

approved