A084923 - OEIS

A084923

Consider the sequence b(1) = n, b(k) is the greatest prime factor of 3*b(k-1)+2. It is conjectured that this always becomes cyclic; a(n) = length of cycle (or 0 if no cycle is reached).

20, 1, 22, 21, 19, 20, 20, 20, 27, 2, 21, 25, 19, 22, 21, 20, 19, 21, 24, 26, 20, 20, 19, 28, 22, 20, 20, 20, 26, 20, 25, 21, 30, 20, 26, 22, 27, 27, 20, 29, 19, 2, 19, 28, 25, 21, 20, 21, 22, 25, 26, 20, 19, 20, 6, 20, 31, 22, 23, 20, 28, 21, 21, 23, 27, 20, 27, 22, 25, 20, 19, 22

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..72.

MATHEMATICA

f[n_] := Flatten[ Table[ # [[1]], {1} ] & /@ FactorInteger[ 3n + 2 ]][[ -1]]; Table[ Length[ NestWhileList[f, n, UnsameQ, All]] - 1, {n, 1, 72}]

CROSSREFS

Cf. A083557.

Sequence in context: A003833 A040418 A140116 * A141589 A162153 A040419

Adjacent sequences: A084920 A084921 A084922 * A084924 A084925 A084926

KEYWORD

nonn

AUTHOR

Robert G. Wilson v & Jud McCranie, Jun 11 2003

STATUS

approved