The 3n + 1 problem is deceptively simple. Consider a function f(n) and a sequence ai where:
| f(n) = | 3n+1 where n is odd |
| n/2 where n is even |
| ai = | n where i = 0 |
| f(ai-1) where i > 1 |
The Collatz conjecture states that ai will become 1 for some i regardless of what value of n is chosen initially. It remains to date a conjecture as there is no proof for it, but there is no counterexample either.