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

%I A087976 #11 Aug 28 2019 03:58:53
%S A087976 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,
%T A087976 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,
%U A087976 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
%N A087976 a(n) = A001221(A025586(n)), the number of distinct prime-factors of maximal term in 3x+1 iteration list started at n.
%H A087976 G. C. Greubel, <a href="/A087976/b087976.txt">Table of n, a(n) for n = 1..1000</a>
%t A087976 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_] :=
%t A087976 Flatten[Table[Take[Sort[Collatz[n], Greater], 1], {n, m}]];
%t A087976 PrimeNu[A025586[100]] (* _G. C. Greubel_, Apr 24 2017 *)
%Y A087976 Cf. A001221, A025586, A087974, A087975.
%K A087976 nonn
%O A087976 1,7
%A A087976 _Labos Elemer_, Sep 25 2003