The **3n + 1 problem** is deceptively simple. Consider a function f(n) and a sequence a_{i} where:

f(n) = | 3n+1 where n is odd |

n/2 where n is even |

a_{i} = |
n where i = 0 |

f(a_{i-1}) where i > 1 |

The **Collatz conjecture** states that a_{i} 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.