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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. 6
0, 0, 2, 0, 1, 0, 1, 4, 3, 0, 1, 0, 3, 4, 2, 0, 3, 0 (list; graph; refs; listen; history; text; internal format)
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

STATUS

approved

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Last modified November 21 11:01 EST 2018. Contains 317447 sequences. (Running on oeis4.)