(notes by Roberto Bigoni)

A number *c _{0}* ≥ 1 generates a

If *C* contains the number 1, this number can be considered the last of
the sequence, because from this number forward the sequence oscillates in the cycle
1-4-2-1.

We may conjecture that **from whatever c_{0}
a Collatz sequence starts, it reaches always 1**.

Even though this conjecture has been tested for many numbers by calculation programs like
the in the above form, **it is not generally demonstrated for every
natural number**.

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Many mathematicians were involved in the search of a demonstration. See:

last reviewed: October 2018