

A230305


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


6



0, 0, 2, 0, 1, 0, 1, 4, 3, 0, 1, 0, 3, 4, 2, 0, 3, 0
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OFFSET

2,3


COMMENTS

If n is a prime, a(n) = 0.
a(20) is presently unknown  see A195265 for the trajectory.


LINKS

Table of n, a(n) for n=2..19.


EXAMPLE

9 > 32 > 25 > 52 > 2213, which is prime, taking 4 steps, so a(9) = 4.


CROSSREFS

Cf. A080670, A195264 (the prime that is reached), A195265, A067599, A037271 (home primes).
Sequence in context: A112517 A112519 A276981 * A091728 A108069 A227837
Adjacent sequences: A230302 A230303 A230304 * A230306 A230307 A230308


KEYWORD

nonn,base,more,hard


AUTHOR

N. J. A. Sloane, Oct 27 2013


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



