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A008876 3x+1 sequence starting at 81. 2
81, 244, 122, 61, 184, 92, 46, 23, 70, 35, 106, 53, 160, 80, 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, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

REFERENCES

Darrell Cox, The 3n + 1 Problem: A Probabilistic Approach, Journal of Integer Sequences, Vol. 15 (2012), #12.5.2.

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 81; 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]&, 81, 100] (* Vincenzo Librandi, Jul 29 2014 *)

PROG

(Haskell)

a008876 n = a008876_list !! n

a008876_list = 81 : iterate a006370 81

-- Reinhard Zumkeller, Aug 30 2012

(MAGMA) [n eq 1 select 81 else IsOdd(Self(n-1)) select 3*Self(n-1)+1 else Self(n-1) div 2: n in [1..70]]; // Vincenzo Librandi, Jul 29 2014

CROSSREFS

Cf. A006370.

Sequence in context: A205055 A255625 A205048 * A031456 A045009 A237167

Adjacent sequences:  A008873 A008874 A008875 * A008877 A008878 A008879

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified December 16 20:28 EST 2018. Contains 318188 sequences. (Running on oeis4.)