The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A230305 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A230305

Iterate A080670 starting at n; a(n) = number of steps to reach a prime, or -1 if no prime is ever reached.
(history; published version)

#16 by Alois P. Heinz at Mon Mar 16 13:03:00 EDT 2020

STATUS

proposed

approved

#15 by Robert Price at Mon Mar 16 11:53:46 EDT 2020

STATUS

editing

proposed

#14 by Robert Price at Mon Mar 16 11:53:26 EDT 2020

MATHEMATICA

fn[n_] := FromDigits[Flatten[IntegerDigits[DeleteCases[Flatten[FactorInteger[n]], 1]]]];

Map[Length, Table[NestWhileList[fn, n, # != 1 && ! PrimeQ[#] &], {n, 2,

19}], {1}] - 1 (* Robert Price, Mar 16 2020 *)

EXTENSIONS

A080670[n_] := FromDigits[Flatten@IntegerDigits[Flatten[FactorInteger@n /. {1 -> {}}]]];

A080670[1] = 1; (* Function A080670 from Robert G Wilson v *)

Table[

If[PrimeQ[n], 0,

test = n; steps = 1;

While[! PrimeQ[test = A080670[test]], steps++];

steps], {n, 2, 19}](* Robert Price, Aug 30 2019 *)

STATUS

approved

editing

#13 by N. J. A. Sloane at Fri Aug 30 21:48:09 EDT 2019

STATUS

proposed

approved

#12 by Robert Price at Fri Aug 30 20:28:42 EDT 2019

STATUS

editing

proposed

#11 by Robert Price at Fri Aug 30 20:28:09 EDT 2019

EXTENSIONS

A080670[n_] := FromDigits[Flatten@IntegerDigits[Flatten[FactorInteger@n /. {1 -> {}}]]];

FromDigits[

Flatten@IntegerDigits[Flatten[FactorInteger@n /. {1 -> {}}]]];

A080670[1] = 1; (* Function A080670 from Robert G Wilson v *)

If[PrimeQ[n], 0,

#10 by Robert Price at Fri Aug 30 20:27:05 EDT 2019

EXTENSIONS

A080670[n_] :=

FromDigits[

Flatten@IntegerDigits[Flatten[FactorInteger@n /. {1 -> {}}]]];

A080670[1] = 1; (*Function A080670 from Robert G Wilson v*)

Table[

If[PrimeQ[n], 0,

test = n; steps = 1;

While[! PrimeQ[test = A080670[test]], steps++];

steps], {n, 2, 19}](* Robert Price, Aug 30 2019 *)

STATUS

approved

editing

#9 by N. J. A. Sloane at Sun Oct 27 02:22:14 EDT 2013

STATUS

editing

approved

#8 by N. J. A. Sloane at Sun Oct 27 02:22:11 EDT 2013

NAME

Iterate A080670 starting at n; a(n) = number of steps to reach a prime that is reached, , or -1 if no prime is ever reached.

COMMENTS

If n is a prime, a(n) = 0.

STATUS

approved

editing

#7 by N. J. A. Sloane at Sun Oct 27 02:20:43 EDT 2013

STATUS

editing

approved