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

Offset: 1

Author

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

Keywords

• nonn

Crossrefs

Cf. A083557.

Programs

Mathematica

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