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3x+1 sequence starting at 87.
5

%I #24 Sep 08 2022 08:44:36

%S 87,262,131,394,197,592,296,148,74,37,112,56,28,14,7,22,11,34,17,52,

%T 26,13,40,20,10,5,16,8,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,

%U 1,4,2,1,4,2,1,4,2,1,4,2,1,4

%N 3x+1 sequence starting at 87.

%D R. K. Guy, Unsolved Problems in Number Theory, E16.

%H Vincenzo Librandi, <a href="/A008879/b008879.txt">Table of n, a(n) for n = 0..200</a>

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

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,1).

%p f := proc(n) option remember; if n = 0 then 87; elif f(n-1) mod 2 = 0 then f(n-1)/2 else 3*f(n-1)+1; fi; end;

%t NestList[If[EvenQ[#], #/2, 3# + 1]&, 87, 100] (* _Vincenzo Librandi_, Jul 29 2014 *)

%o (Magma) [n eq 1 select 87 else IsOdd(Self(n-1)) select 3*Self(n-1)+1 else Self(n-1) div 2: n in [1..80]]; // _Vincenzo Librandi_, Jul 29 2014

%Y Cf. similar sequences listed in A245671.

%Y Row 87 of A347270.

%K nonn

%O 0,1

%A _N. J. A. Sloane_.