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A198724 Let P(n) be the maximal prime divisor of 3*n+1. Then a(n) is the smallest number of iterations of P(n) such that the a(n)-th iteration < n, and a(n) = 0, if such number does not exist. 0
2, 3, 1, 6, 4, 1, 1, 6, 3, 2, 1, 2, 2, 1, 1, 1, 2, 3, 1, 3, 1, 2, 1, 2, 6, 1, 1, 1, 4, 3, 1, 2, 2, 3, 1, 1, 5, 1, 1, 3, 1, 1, 1, 2, 3, 1, 1, 3, 1, 6, 1, 2, 2, 1, 1, 1, 4, 2, 1, 1, 1, 2, 1, 2, 2, 1, 1, 3, 2, 1, 1, 2, 2, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 3, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

Question. Is the sequence bounded?

By private communication from Alois P. Heinz, the places of records are 3, 4, 6, 286, 29866 with values 2, 3, 6, 8, 10. No more up to 46000000.

LINKS

Table of n, a(n) for n=3..88.

V. Shevelev, Collatz-like problem with prime iterations

EXAMPLE

For n=52 we have iterations: P^(1)=157, P^(2)=59, P^(3)=89, P^(4)=67, P^(5)=101, P^(6)=19<52. Thus a(52)=6.

MATHEMATICA

P[n_] := FactorInteger[3*n + 1][[-1, 1]]; Table[k = 1; m = n; While[m = P[m]; m >= n, k++]; k, {n, 3, 100}] (* T. D. Noe, Oct 30 2011 *)

PROG

(PARI) a(n) = {nb = 1; na = n; while((nna=vecmax(factor(3*na+1)[, 1])) >= n, na = nna; nb++); nb; } \\ Michel Marcus, Feb 06 2016

CROSSREFS

Cf. A074473, A126241.

Sequence in context: A166295 A016730 A114576 * A223486 A263294 A205112

Adjacent sequences:  A198721 A198722 A198723 * A198725 A198726 A198727

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Oct 29 2011

STATUS

approved

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Last modified November 21 16:27 EST 2017. Contains 295003 sequences.