The Hailstone Sequence

Question P2.5.7

The hailstone sequence starting at an integer $n > 0$ is generated by the repeated application of the three rules:

  • if $n=1$, the sequence ends;
  • if $n$ is even, the next number in the sequence is $n/2$;
  • if $n$ is odd, the next number in the sequence is $3n+1$.

(a) Write a program to calculate the hailstone sequence starting at 27.

(b) Let the stopping time be the number of numbers in a given hailstone sequence. Modify your hailstone program to return the stopping time instead of the numbers themselves. Adapt your program to demonstrate that the hailstone sequences started with $1 \le n \le 100$ agree with the Collatz conjecture (that all hailstone sequences stop eventually).


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