A290328 Iterate the map x -> A289667(x) starting at n; sequence gives number of steps to reach a prime, or -1 if no prime is ever reached.

0, 0, 4, 0, 3, 0, 3, 1, 1, 0, 7, 0, 2, 2, 20, 0, 19, 0, 5, 2, 19, 0, 4, 1, 1, 52, 1, 0, 51, 0, 1, 2, 1, 2, 1, 0, 1, 4, 51, 0, 2, 0, 1, 20, 5, 0

Offset: 2

Author

Chai Wah Wu, Jul 27 2017

Keywords

• nonn
• more
• base

Comments

Base 3 analog of A230626. See A290350 for the trajectory of 48.

If a(48) != -1, then a(48) > 120. - Chai Wah Wu, Jul 29 2017

Crossrefs

Cf. A289667, A230626, A195264, A290350, A290329.

Programs

Mathematica

Table[-1 + Length@ NestWhileList[FromDigits[#, 3] &@ Flatten@ Map[IntegerDigits[#, 3] &, FactorInteger[#] /. {p_, e_} /; p > 0 :> If[e == 1, p, {p, e}]] &, n, ! PrimeQ@ # &], {n, 2, 47}] (* Michael De Vlieger, Jul 29 2017 *)