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A230627 Prime reached in A230626, or -1 if no prime is reached. 11
2, 3, 31, 5, 11, 7, 11, 23, 31, 11, 43, 13, 23, 29, 251, 17, 23, 19, 251, 31, 43, 23, 47, 43, 463, 29, 23, 29, 127, 31, 31, 59, 23, 47, 8093, 37, 83, 61, 127, 41, 179, 43, 467, 463, 23, 47, 83, 127, 467, 113, 173, 53, 47, 23, 179, 241, 127, 59, 349, 61, 179 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,1
COMMENTS
David J. Seal found that the number 255987 is fixed by the map described in A230625 (or equally A287874), so a(255987) = -1. - N. J. A. Sloane, Jun 15 2017
I also observe that the numbers 1007 and 1269 are mapped to each other by that map, as are the numbers 1503 and 3751 (see the b-file submitted by Chai Wah Wu for A230625). So a(1007) = a(1269) = a(1503) = a(3751) = -1. - David J. Seal, Jun 16 2017
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). - Chai Wah Wu, Jun 16 2017
See A287878 for the trajectory of 234. - N. J. A. Sloane, Jun 17 2017
See A288894 for the trajectory of 3932. - Sean A. Irvine, Jun 18 2017
The latest information seems to be that for numbers less than 12388, all trajectories either end at a fixed point or in a cycle of length 2. - N. J. A. Sloane, Jul 27 2017
LINKS
Sean A. Irvine, Table of n, a(n) for n = 2..10000 (terms 2..3931 from Chai Wah Wu)
N. J. A. Sloane, Confessions of a Sequence Addict (AofA2017), slides of invited talk given at AofA 2017, Jun 19 2017, Princeton. Mentions this sequence.
N. J. A. Sloane, Three (No, 8) Lovely Problems from the OEIS, Experimental Mathematics Seminar, Rutgers University, Oct 05 2017, Part I, Part 2, Slides. (Mentions this sequence)
MATHEMATICA
fn[n_] := FromDigits[Flatten[IntegerDigits[ReplaceAll[FactorInteger[n], {x_, 1} -> {x}], 2]], 2];
Table[NestWhile[fn, n, # != 1 && ! PrimeQ[#] &], {n, 2, 50}] (* Robert Price, Mar 16 2020 *)
CROSSREFS
Base-2 analog to A195264.
See A287875 for these same numbers written in binary.
See A288847 for where the values -1 occur.
Sequence in context: A270483 A217370 A088115 * A048986 A093712 A035514
KEYWORD
sign,base
AUTHOR
N. J. A. Sloane, Oct 27 2013
EXTENSIONS
More terms from Chai Wah Wu, Jul 15 2014
Changed the "escape" value from 0 to -1 to be consistent with A195264. - N. J. A. Sloane, Jul 27 2017
STATUS
approved

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Last modified July 18 10:00 EDT 2024. Contains 374378 sequences. (Running on oeis4.)