A008877 3x+1 sequence starting at 57.

57, 172, 86, 43, 130, 65, 196, 98, 49, 148, 74, 37, 112, 56, 28, 14, 7, 22, 11, 34, 17, 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, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1

Offset

0,1

References

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

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Index entries for sequences related to 3x+1 (or Collatz) problem

Index entries for linear recurrences with constant coefficients, signature (0,0,1).

Maple

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;

Mathematica

NestList[If[EvenQ[#], #/2, 3# + 1]&, 57, 100] (* Vincenzo Librandi, Jul 29 2014 *)

Prog

(Haskell)
a008877 n = a008877_list !! n
a008877_list = 57 : iterate a006370 57
-- Reinhard Zumkeller, Aug 30 2012
(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

Crossrefs

Cf. A006370.

Row 57 of A347270.

Sequence in context: A356423 A044389 A044770 * A338078 A336191 A277805

Adjacent sequences: A008874 A008875 A008876 * A008878 A008879 A008880

Keyword

nonn

Author

N. J. A. Sloane.

Status

approved