Skip to main content
12 events
when toggle format what by license comment
Jan 1, 2023 at 4:05 comment added Robbie Goodwin Why, please, are you Asking that without Posting helpful research? After which number did you give up your own search?
Dec 31, 2022 at 19:02 history edited YCor CC BY-SA 4.0
made title more specific
Dec 31, 2022 at 18:48 vote accept Nandakumar R
Dec 31, 2022 at 18:47 comment added Nandakumar R Sure. Moved qn 2 to another post
Dec 31, 2022 at 18:45 history edited Nandakumar R CC BY-SA 4.0
deleted 225 characters in body; edited title
Dec 31, 2022 at 16:53 history became hot network question
Dec 31, 2022 at 14:48 comment added GH from MO Please restrict to one question per post. This is standard policy on this website.
Dec 31, 2022 at 12:57 history edited Martin Sleziak
edited tags
Dec 31, 2022 at 12:53 answer added Ofir Gorodetsky timeline score: 47
Dec 31, 2022 at 11:38 comment added Ofir Gorodetsky Heuristically, $F_{n}\pm 1$ are simultaneously primes with probability $\asymp 1/n^2$ since $F_n$ grows exponentially and the density of primes is $1/\log x$. The convergence of $1/n^2$ suggests a finite number of such sandwiched Fibonaccis. Twin primes $(p,p+2)$ must satisfy $p\equiv -1 \bmod 6$, so a sandwiched Fibonacci number must be divisible by $6$. Since $F_n$ is periodic modulo $6$, a short computation shows $F_n \equiv 0 \bmod 6$ if and only if $n \equiv 0 \bmod 12$. I couldn't even find $n$ for which not both $F_{12n}-1,F_{12n}+1$ are composite.
Dec 31, 2022 at 11:37 comment added Ofir Gorodetsky Can you find a Fibonacci number $F_n>10$ for which $F_{n}+1$ is a prime?
Dec 31, 2022 at 8:49 history asked Nandakumar R CC BY-SA 4.0