Questions on the Fibonacci numbers, a special sequence of integers that satisfy the recurrence $F_n=F_{n-1}+F_{n-2}$ with the initial conditions $F_0=0$ and $F_1=1$.

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14
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4answers
409 views

Converting recursive equations into matrices

How do we convert recursive equations into matrix forms? For instance, consider this recursive equation(Fibonacci Series): $$F_n = F_{n-1} + F_{n-2}$$ And it comes out to be that the following that ...
1
vote
1answer
72 views

Fibonacci numbers $F_{n+3} + F_{n} = 2F_{n+2}$

Prove $F_{n+3} + F_{n} = 2F_{n+2}$ for any positive integer n. So What I did was this: fn+ fn+1 = fn+2 fn + fn+1 = fn+2 => fn+2 -fn+1 fn+1 + fn+2 = fn+3 then I subsituted into equation in ...
2
votes
5answers
2k views

What is the summation notation for the Fibonacci numbers?

I learned about summation notation the other day, and I'm looking for a way to write the Fibonacci numbers with it. What would it look like?
2
votes
2answers
58 views

Why is $\sum_{k=0}^{n} f(n,k) = F_{n+2}$?

If $f(n,k)$ is the number of $k$ size subsets of $[ n ] = { 1 , \ldots , n }$ which do not contain a pair of consecutive numbers, how can I show that $\sum_{k=0}^{n} f(n,k) = F_{n+2}$? ($F_{n}$ is the ...
1
vote
4answers
135 views

Fibonacci Calculation using a larger matrix

So the formula to generate the fibonacci sequence in matrix form is: $$ \begin{pmatrix} 1 & 1 \\ 1 & 0 \\ \end{pmatrix}^n = \begin{pmatrix} F_{n+1} & F_n \\ F_n & ...
2
votes
2answers
95 views

How do I apply the $\pm4$ part of the equation $5F_n^2\pm~4=L_n^2$ without knowing $n$?

I'm trying to test a great many numbers $a^3+b^3$ to see if any of them are Fibonacci using the formula $$a^3+b^3=F_n \iff 5(a^3+b^3)^2\pm~4=L_n^2$$ I want to make my search more efficient by having ...
11
votes
5answers
1k views

How to tell if a Fibonacci number has an even or odd index

Given only $F_n$, that is the $n$th term of the Fibonacci sequence, how can you tell if $n \equiv 1 \mod 2$ or $n \equiv 0 \mod 2$? I know you can use the Pisano period, however if $n \equiv 1$ or ...
0
votes
1answer
169 views

Base case in the Binet formula (Proof by strong induction)

I don't understand why the author says that the inductive formula does not apply until $u_3$. The formula does not depend on other terms in the Fibonacci sequence, so I thought I could just prove it ...
1
vote
2answers
72 views

How to establish this inequality without using induction?

Given the Fibonacci sequence $a_1 = 1$, $a_2 = 2$, $\ldots$, $a_{n+1} = a_n + a_{n-1} $ for $n \geq 2$, how to derive, without using induction, the inequality $$ a_n < (\frac{1+\sqrt{5}}{2})^n $$ ...
1
vote
0answers
336 views

Calculating Pisano periods for any integer

I recently stumbled across this SPOJ question: http://www.spoj.com/problems/PISANO/ The question is simple. Calculate the Pisano period of a number. After I researched my way through the web, I found ...
5
votes
1answer
95 views

Number of zeros in Fibonacci sequences mod $p$

We know that Fibonacci sequences are periodic in mod $m$. For example, for $p\equiv \pm 1 \pmod 5$ and $\pm 2 \pmod 5$ the periods for Fibonacci sequences modulo $p$ divide $p-1$ and $2p+2$ ...
3
votes
1answer
120 views

Fibonacci series mod a number

I'm trying to write a program with an input of numbers $n$ and $k$ (where $n<10^{20}$ and $k<10^9$), where I compute fib[n] % k. What is a good FAST way of computing this? I have read many ...
1
vote
1answer
112 views

What is length of period of fibonacci number mod 1000033

Can some explain me how the period of Fibonacci mod $1000033$ is $4684$. As we know if $n$ mod $5$ is $2$ or $3$ then period is $2n + 2$ so the period should me $2\times1000033 + 2$ but why it is ...
-1
votes
1answer
180 views

Asymptotic value of Fibonacci numbers

It is well known that $F_n\sim\frac{\phi^n}{\sqrt{5}}$, where $\phi=\frac{1+\sqrt{5}}{2}$. Does someone know a better estimate? With proof please. I'm trying to calculate the following limit: Let ...
0
votes
1answer
73 views

Let $u_n$ be the $n$-th entry in the Fibonacci sequence $1,1,2,3,5,8,13,\ldots$

If you start with $u_1 = 1$ and $u_2 = 1$, then the sequence can be generated using the formula $$u_{n+1} = u_n + u_{n-1}\ .$$ If $u_n = r^n$, what is r? Can anyone figure this out? I am so stuck ...
4
votes
2answers
162 views

The sum of $n$ consecutive Fibonacci numbers.

The sum of $8$ consecutive Fibonacci numbers is divisible by $3$. How can I generalize this for the sum of $n$ consecutive Fibonacci numbers? For example, $$1+1+2+3+5+8+13+21=54=3\times 18 \\ ...
1
vote
1answer
67 views

Proof that golden angle successively divides the largest gap by the golden ratio?

The golden angle divides the circumference of a circle by the golden ratio. "If radial spokes are placed successively into the circle, each spaced by a golden angle increment, then each additional ...
32
votes
4answers
589 views
1
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4answers
216 views

Determine which Fibonacci numbers are even

(a) Determine which Fibonacci numbers are even. Use a form of mathematical induction to prove your conjecture. (b) Determine which Fibonacci numbers are divisible by 3. Use a form of mathematical ...
1
vote
4answers
48 views

Help understanding Recursive algorithm question

We have a function that is defined recursively by $f(0)=f_0$, $f(1)=f_1$ and $f(n+2) = f(n)+f(n+1)$ for $n\geq0$ For $n\geq0$, let $c(n)$ be the total number of additions for calculating $f(n)$ ...
2
votes
1answer
59 views

What's the Lucas version of the Möbius test for Fibonacci numbers?

I recently came across the following, attributed to Möbius: $$(a\in\mathbb N)=F_n\iff\left[\varphi a-\tfrac{1}{a},\varphi a+\tfrac{1}{a}\right]\ni(b\in\mathbb N)$$ It is the lesser-known test used to ...
1
vote
1answer
34 views

What is the Lucas counterpart to the Fibonacci identity $5F_n^2\pm~4=\lambda^2$?

It's a well-known rule that a number $x$ belongs to the Fibonnaci Sequence iff: $$\begin{align}5x^2\pm~4&=\lambda^2&\lambda\in\mathbb Z\end{align}$$ In other words, if and only if $5x^2\pm~4$ ...
1
vote
2answers
59 views

Compute $F_{1000} \bmod F_{11}$, where $F_n$ denote the Fibonacci numbers

Compute $F_{1000} \bmod F_{11}$, where $F_n$ denote the Fibonacci numbers. Progress: $F_{11}=89$ . I believe you should find the period of $F_n \bmod 89$ and use that to solve it. But I'm not not ...
0
votes
1answer
38 views

finding $n$ consecutive composite Fibonacci numbers.

For each $n$, How can we find $n$ consecutive composite Fibonacci numbers?
2
votes
3answers
97 views

Is it true that $5^k \mid f(5^k)$?

I guess if it is true that $5^k \mid f(5^k)$, where $f(n)$ denotes the $n$-th Fibonacci's number. I have tried to prove it by induction on $k$, but nothing. Have you got any ideas?
2
votes
1answer
37 views

Is a Lucas Number with either a power of 2 or a prime index always coprime with all previous Lucas Numbers?

I was looking at this webpage which lists the first 200 Lucas Numbers color-coded with their prime factors and I noticed that all the Lucas numbers with power of two or prime indexes were relatively ...
1
vote
1answer
70 views

Compute $F_{1000} \bmod 1001$, where $F_n$ denote the Fibonacci numbers

Compute $F_{1000} \bmod 1001$, where $F_n$ denote the Fibonacci numbers. I have tried using the fact that $F_{n^k} \bmod F_n = 0, k=1,2,3,...$ but that doesn't get me anywhere. Thanks!
3
votes
0answers
54 views

Are $1$ and $3$ the only numbers of the form $2^n-1$ that exist in the Fibonacci sequence? [duplicate]

Are $1$ and $3$ the only numbers of the form $2^n-1$ that exist in the Fibonacci sequence? Then, if they are not the only ones, are there infinite cases? I have tried finding another example using a ...
0
votes
1answer
69 views

Function relating Euler's constant and the golden ratio

Okay, I was messing around on Excel with some coefficients and I stumbled onto this. Not sure if it converges but it gets pretty damn close around the 1024th term mark. Was wondering if somebody could ...
0
votes
1answer
42 views

Help with a proof involving Fibonacci numbers.

I'm working through SICP MIT course, and I'm a little lost on how to prove the following statement. I think I'm able to demonstrate it, but have no idea how to prove this statement. I may ...
1
vote
2answers
115 views

Non integer Fibonacci numbers

I'm pretty sure we're all familiar with the Fibonacci sequence. Most people with more than passing knowledge of this most marvelous gem are aware of the Binet formula, $Fib(n) = (\varphi^n - ...
8
votes
2answers
277 views

Interpolated Fibonacci numbers - real or complex?

The common Binet-formula for the Fibonacci-numbers $$ f_n = {\varphi^n- (1-\varphi)^n \over \sqrt 5 } \small {\qquad \qquad \text{ where }\varphi={1+\sqrt 5\over 2}}$$ allows interpolation to ...
1
vote
2answers
100 views

How many $a$-nary sequences of length $b$ never have $c$ consecutive occurrences of a digit?

Let $S(a,b,c): = \#\{a$-nary sequences of length $b$ without $c$ consecutive occurrences of a digit$\}$. For example, $S(2,n,3)$ would be the number of binary sequences of length $n$ without $3$ ...
-3
votes
2answers
982 views

Expressing Fibonacci numbers as the sum of squares.

As we know that by observation, the Fibonacci numbers ($F_0=0$, $F_1=1$, $F_{n}=F_{n-1}+F_{n-2}$) have the identity $$F_{2k+1}=F_k^2 + F_{k+1}^2.$$ In particular, if $n$ is odd, then $F_n$ is a sum of ...
2
votes
2answers
85 views

Fibonacci combinatorial identity

Can someone explain how to prove the following identity involving Fibonacci sequence $F_n$ $F_{2n} = {n \choose 0} F_0 + {n\choose 1} F_1 + ... {n\choose n} F_n$ ?
8
votes
3answers
135 views

Asking About Binomial Sum Related to Fibonacci

How would I prove $$ \sum\limits_{i,j\ge 0} {n-i \choose j} {n-j \choose i}=F_{2n+1} $$ where $n$ is a nonnegative integer and $\{F_n\}_{n\ge 0}$ is a sequence of Fibonacci numbers? Thank you very ...
1
vote
1answer
74 views

Does this mean some Wall-Sun-Sun primes have already been found?

In the PrimeGrid project statistics page for Wall-Sun-Sun Prime Search, it says, Wall-Sun-Suns ... 2 Near Wall-Sun-Suns ... 208 However, all the internet search ...
2
votes
0answers
71 views

Fibonacci applied to human population living to dead ratio problem

If this forum is not the right one for my question, please redirect it. I do not know where to ask it. The question might seem tongue-in-cheek, believe me it's not! Last week to occupy my mind, I ...
1
vote
2answers
57 views

Help with a proof I can't quite

Let $(F_j)^\infty_{j=1}$ be the sequence of Fibonacci numbers. For all $n \in \mathbb{N}$, $\sum\limits_{k=1}^{2n-1}F_kF_{k+1}=(F_{2n})^2$. I handled the base case quite well but couldn't go very ...
3
votes
1answer
150 views

Magic Squares with Lucas and Fibonacci Numbers

I am quite curious about can we construct magic squares using only Lucas and Fibonacci numbers(of course not repeating them? If yes, how can we construct them? And if not , what is the proof?
0
votes
1answer
30 views

Inequality of Lucas Numbers

Can it be shown that \begin{align} \frac{1}{\ln(1+L_{n}) -1} \geq \frac{L_{n}}{(L_{n}-1)(e^{L_{n}}-1)} \end{align} where $L_{n}$ is the $n^{th}$ Lucas number. Show results in full detail.
1
vote
0answers
83 views

Linear combination of numbers: Express the $n^{th}$ Fibonacci number in terms of known constants.

Given the concept that any number can be expressed as a combination of other numbers can the $n^{th}$ Fibonacci number be expressed in terms of $\zeta(3)$ and $\ln(2/e)$ ? If possible, show all work ...
4
votes
2answers
500 views

Number of Fibonacci numbers in a range

The definition of the Fibonacci numbers is given by: $$\begin{align}f_1 &= 1;\\ f_2 &= 2;\\ f_n &= f_{n-1} + f_{n-2},\qquad (n >= 3); \end{align}$$ now we are given two numbers $a$ ...
1
vote
4answers
112 views

Summation of Fibonacci numbers $F_n$ with $n$ odd vs. even

Compare the summation below: $$\begin{align} \smash[b]{\sum_{i=1}^n F_{2i-1}}&=F_1+F_3+F_5+\cdots+F_{2n-1}\\ &=1+2+5+\cdots+F_{2n-1}\\ &=F_{2n}\\ \end{align} $$ with this one: ...
3
votes
1answer
100 views

Using matrices to calculate fibonacci?

I have been told a couple of times it possible to calculate the fibonacci sequence much quicker using matrices but I never understood/they never elaborated. Would somebody be able to show how this ...
3
votes
2answers
154 views

Check if the number is a result of multiplying two fibonacci numbers

Is there a way to check if a given number is a result of multiplication of two fibonacci numbers? Any theory/characteristics allowing to quickly decline some of these given numbers?
5
votes
2answers
1k views

How to prove Fibonacci sequence with matrices?

How do you prove that: $$ \begin{pmatrix} 1 & 1\\ 1 & 0 \end{pmatrix}^n = \begin{pmatrix} F_{n+1} & F_n\\ F_{n} & F_{n-1} \end{pmatrix}$$
0
votes
0answers
25 views

Fibonacci binary (only 1's and 0's) how to get it

i know what fibonacci numbers are $ F_{n+2}=F_{n+1}+F_{n} $ but what is the case of fibonacci binary string which has only 1 and 0 ? how could i get this string :D is just taking the fibonacci ...
1
vote
2answers
287 views

Modular Fibonacci series

My second observation is the following. Let $p$ be a prime not equal to $5$. Then $5$ is a quadratic residue modulo $p$ if and only if $p\equiv\pm1\pmod5$. And $5$ is not a quadratic residue modulo ...
0
votes
0answers
23 views

Relation between series and equations

There is following quotes from wiki on Plastic number: The powers of the plastic number $A(n) = ρ^n$ satisfy the recurrence relation $A(n) = A(n − 2) + A(n − 3)$ for $n > 2$. And 2nd is that ...