A087976 a(n) = A001221(A025586(n)), the number of distinct prime-factors of maximal term in 3x+1 iteration list started at n.

0, 1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 2, 2, 2, 1, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 3, 1, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2

Offset: 1

Author

Labos Elemer, Sep 25 2003

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A001221, A025586, A087974, A087975.

Programs

Mathematica

Collatz[a0_Integer, maxits_: 1000] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, a0, Unequal[#, 1, -1, -10, -34] &, 1, maxits]; (*Collatz[n] function definition by Eric Weisstein*) A025586[m_] :=
Flatten[Table[Take[Sort[Collatz[n], Greater], 1], {n, m}]];
PrimeNu[A025586[100]] (* G. C. Greubel, Apr 24 2017 *)