%I #26 Sep 08 2022 08:44:36
%S 57,172,86,43,130,65,196,98,49,148,74,37,112,56,28,14,7,22,11,34,17,
%T 52,26,13,40,20,10,5,16,8,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,
%U 2,1,4,2,1,4,2,1,4,2,1,4,2,1
%N 3x+1 sequence starting at 57.
%D R. K. Guy, Unsolved Problems in Number Theory, E16.
%H Vincenzo Librandi, <a href="/A008877/b008877.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 57; 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]&, 57, 100] (* _Vincenzo Librandi_, Jul 29 2014 *)
%o (Haskell)
%o a008877 n = a008877_list !! n
%o a008877_list = 57 : iterate a006370 57
%o -- _Reinhard Zumkeller_, Aug 30 2012
%o (Magma) [n eq 1 select 57 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. A006370.
%Y Row 57 of A347270.
%K nonn
%O 0,1
%A _N. J. A. Sloane_.