# I Is this a Fibronacci sequence

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1. Nov 16, 2016

### Ling Min Hao

Is the series of numbers 2,3,5,8,13,21 ... a fibronacci sequence ? Because it doesnt start with 1 , but it fulfills the explicit formula .

2. Nov 16, 2016

### PeroK

How do you define a Fibonacci sequence?

3. Nov 16, 2016

### Ling Min Hao

I dont know , but from wikipedia , it says Fibronacci starts from either 0,1 or 1,1 but is 2,3,5,8,13,21... a Fibronacci sequence it remains unknown for me ..

4. Nov 16, 2016

### Staff: Mentor

I guess it depends on author and purpose whether only the classical sequence is meant or all possible. I looked up "generalized Fibonacci sequence" and found, e.g. http://www.maths.surrey.ac.uk/hosted-sites/R.Knott/Fibonacci/fibGen.html

As so often the key lies in the question: What's your goal? Usually "a Fibonacci sequence" simply has to obey $F_{n+1} = F_n + F_{n-1}$. Initial values result in different sequences. If someone speaks about "the Fibonacci sequence $F_n$" he probably means the one starting with $(0,1)$. Generalized ones should clearly by stated as such, which often can be recognized the way they define the initial values: $(F_0,F_1)=(a_0,a_1)$ indicates the usage of generalized ones. Formulas which contain $F_n$ without any further explanation probably refer to the classic sequence only.

5. Nov 16, 2016

### PeroK

A question like this is entirely definition dependent. If you allow a Fibonacci sequence to have any two initial terms, then it is. If not, then it's not. Or, in this case, it is simply not the full sequence.

6. Nov 25, 2016