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Questions on the Lucas numbers, a special sequence of integers that satisfy the recurrence $L_n=L_{n-1}+L_{n-2}$ with the initial conditions $L_0=2$ and $L_1=1$.

100 questions
0 votes 1 answer 34 views

Lucas numbers relation to Φ

So, the Lucas numbers are 2,1,3,4,7,11... Let L(n) be nth lucas number Fibonacci numbers are 1,1,2,3,5,8,13,21... Φ^n=F(n+1)+F(n-1), F=Fibonacci number and n=nth So, if I say n=5, then Φ^n=F(6)+F(4)=... user avatar Aveer
  • 1
1 vote 0 answers 46 views

Generalizing Fibonacci/Lucas-like series' in terms of the Fibonacci Sequence

(TLDR: I independently discovered a property of Fibonacci-like sequences and I couldn't have been the first one to notice. Who else has?) For some background, I haven't been in a math class since high-... user avatar Justin Reeves
  • 11
1 vote 2 answers 49 views

Closed form representation for $\sum_{k=0}^{\lfloor n/2 \rfloor} \binom{n-k}k$

Answering some other question, I stumbled upon the following relationship: For $n\in\Bbb N$ let $$p_n = \sum_{k=0}^{\lfloor n/2 \rfloor} \binom{n-k}k$$ and let $$a_n = p_n+p_{n-2}\quad \text{ if } n \... user avatar emacs drives me nuts
  • 5,164
1 vote 0 answers 40 views

How to prove that $a_{2n} = a_nb_n$ in a Lucas sequence? [duplicate]

Here's the question in in my book: Define $(b_n)$ by $b_1=1$, $b_n = a_{n+1}+a_{n-1}$ for $n ≥ 2$. $(b_n)$ is known as the sequence of Lucas numbers. Prove (i) $b_n = b_{n-1} + b_{n-2}$ for $n ≥ 3$. (... user avatar Tanmay Gupta
  • 13
0 votes 0 answers 22 views

How to find the count of edge covers of a graph of degree 2?

I have been trying to understand this editorial for question F of Atcoder beginner contest 247: . What I have not been able to understand is this part:... user avatar black.swordsman
  • 1
5 votes 1 answer 214 views

A pattern of periodic continued fraction

I am interested in the continued fractions which $1$s are consecutive appears. For example, it is the following values. $$ \sqrt{7} = [2;\overline{1,1,1,4}] \\ \sqrt{13} = [3;\overline{1,1,1,1,6}] $$ ... user avatar isato
  • 416
0 votes 0 answers 10 views

Convert LUC formula to GF2 polynomial base

is it possible to convert LUC public key encryption formula from standard math to finite field GF(2) polynomial like RSA? LUC is based on Lucas function and it uses the following equation V(i+1)=mv(i)-... user avatar Zaid Alani
  • 1
1 vote 1 answer 104 views

Primality test for numbers of the form $(10^p-1)/9$ (and maybe $((10 \cdot 2^n)^p-1)/(10 \cdot 2^n-1)$)

This question is successor of Primality test for numbers of the form (11^p−1)/10 Here is what I observed: For $(10^p-1)/9$ : Let $N$ = $(10^p-1)/9$ when $p$ is a prime number $p > 3$. Let the ... user avatar kijinSeija
  • 313
4 votes 1 answer 171 views

If $(3p_n\pm \sqrt{5p_n^2-4})\Delta/(2p_n)$ is an integer then $p_n$ is an odd-indexed Fibonacci number

Suppose $1<p_1<\dots<p_n$ are pairwise relatively prime integers and let $\Delta=p_1\cdots p_n$. In the proof of Lemma 4.8 of this paper (), there is the ... user avatar user302934
  • 2,130
2 votes 2 answers 47 views

Proof recursion is a subset of Lucas numbers

I need to prove that the recursion $a_n=\frac{a_{n-1}^2+5}{a_{n-2}}$ for $a_0=2,a_1=3$ are the Lucas numbers with even index. I would like to use induction, but I got a fraction that I'm not sure how ... user avatar rkai
  • 39
0 votes 1 answer 73 views

How can this relation between Lucas and Fibonacci numbers be proved? [closed]

$ \lim_{n \to \infty}\Bigg(\dfrac{2 \cdot 10^n + 1 \cdot 10^{n-1} + 3 \cdot 10^{n-2} + 4 \cdot 10^{n-3}+...}{0\cdot 10^n + 1 \cdot 10^{n-1} + 1 \cdot 10^{n-2} + 2 \cdot 10^{n-3}+...}\Bigg) = 19 $ I ... user avatar Amalac
  • 27
2 votes 1 answer 44 views

How to find a complementary subspace for the subspace of sequences where $u_{n+2}=u_{n} + u_{n+1}$, in $\mathbb{R}^\infty$?

Consider this subspace of $\mathbb{R}^\infty$ (sequences of real numbers): $U = \{\vec{u} = (u_1, u_2, ...) \in \mathbb{R}^\infty | u_{i+2} = u_i + u_{i+1}$ for all $i\}$ My question is: how can i ... user avatar william_grisaitis
  • 288
1 vote 0 answers 176 views

A Lucas sequence

Define a recursive sequence $\{x_n\}$ as follows $$x_0=2,x_1=3,x_n=\frac{x_{n-1}^2+5}{x_{n-2}}(n\ge2).$$ Prove $x_n$ is a prime if and only if $n=0$ or $n=2^k$ where $k\in \mathbb{N}.$ Note that \... user avatar mengdie1982
  • 12.7k
0 votes 1 answer 55 views

Does $(L_{p+1}+2)\equiv0 \mod p$ only when $p^2$ have digits in nondecreasing order?

Let $L_n$ be the $n$th Lucas number and $p$ a prime number. I noticed something with Lucas Number : it seems than $(L_{n+1}+2)\equiv0 \mod n$ is right only when $n$ is a prime $p$ and only if $p^2$ ... user avatar kijinSeija
  • 313
10 votes 0 answers 171 views

When is $L_n-1$ a prime?

Let $L_n$ be the $n$th Lucas number. I tested whether $L_n-1$ is prime for all $n<100000$ and found that it is prime only for $n=2,3,6,24,48,96$. Are there any other prime numbers? Also, is there a ... user avatar dodicta
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