Problem #14

The 3n+1 Problem
Public 09/25/09 6xp Programming 63.6%

Consider the following algorithm:

1. input n

2. print n

3. if n = 1 then STOP

4. if n is odd then n <-- 3n + 1

5. else n <-- n/2

6. GOTO 2

Given the input 22, the following sequence of numbers will be printed 22 11 34 17 52 26 13 40 20 10 5 16 8 4 2 1

It is conjectured that the algorithm above will terminate (when a 1 is printed) for any integral input value. Despite the simplicity of the algorithm, it is unknown whether this conjecture is true. It has been verified, however, for all integers n such that 0 < n < 1,000,000 (and, in fact, for many more numbers than this.)

Given an input n, it is possible to determine the number of numbers printed (including the 1). For a given n this is called the cycle-length of n. In the example above, the cycle length of 22 is 16.

For any two numbers i and j you are to determine the maximum cycle length over all numbers between i and j.(inclusive)

What is the answer if i=1 j=1000000 ?


You need to be a member to keep track of your progress.

Time may end, but hope will last forever.

Other Challenge Sites