This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified October 22 10:17 EDT 2019. Contains 328315 sequences. (Running on oeis4.)