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Largest odd prime in sequence obtained in 3x+1 (or Collatz) problem starting at n, or 0 if no such prime is found.
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%I #19 Aug 14 2024 01:54:02

%S 0,0,5,0,5,5,17,0,17,5,17,5,13,17,53,0,17,17,29,5,0,17,53,5,29,13,

%T 1619,17,29,53,1619,0,29,17,53,17,37,29,101,5,1619,0,43,17,17,53,1619,

%U 5,37,29,29,13,53,1619,1619,17,43,29,101,53,61,1619,1619,0,37,29,101,17,13

%N Largest odd prime in sequence obtained in 3x+1 (or Collatz) problem starting at n, or 0 if no such prime is found.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/CollatzProblem.html">Collatz Problem</a>

%H <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a>

%t op[n_]:=Module[{lst=NestWhileList[If[EvenQ[#],#/2,3#+1]&,n,#!=1&],m}, m= Max[Select[ lst,PrimeQ]];If[m<3,0,m]]; Array[op,70] (* _Harvey P. Dale_, Apr 30 2011 *)

%Y Cf. A055509, A087272.

%K nonn

%O 1,3

%A _G. L. Honaker, Jr._, Jun 30 2000

%E More terms from Larry Reeves (larryr(AT)acm.org), Aug 09 2001