The following question goes by several names, the Collatz Algorithm, the Syracuse Problem, or sometimes just the 3n+1-problem,and it is simply the observation that, observation that, beginning any number n, the following process always seems to end with the number 1.
If n is even divide it by 2, while if n is odd, replace it by 3n+1.
For example, beginning with n = 7 we are led by rules through the following sequence:
And so the conjecture is true for n=7 , and indeed it has been verified for all n up beyond a million million. Things are different if you fiddle with the rules: for instance, replacing 3n+1 by 3n-1 results in cycle:
The sequence of numbers that arise from these calculations behave like hailstones in that they rise and fall erratically over a long period eventually, it seems,always hit the ground.