Let $F_n$ be the $n$ th Fibonacci-number and define $$f(n):=F_{n^2}-F_n+1$$
For most integers $n>1$ , $f(n)$ has a small prime factor :
2 3
3 3
4 5
5 3
6 5
7 11
8 227
9 3727
10 3
11 3
12 5
13 3
14 2099
15 307
16 7445729
17 11
18 3
19 3
20 197921
21 3
22 137
23 11
24 5
25 103681
26 3
27 3
28 81209593
29 3
30 547
31 17
32 5
33 11
34 3
35 3
36 701
37 3
38 5
39 647
40 353
41 17
42 3
43 3
44 5
45 3
46 5
47 11
48 40759
49 79
50 3
51 3
52 5
53 3
54 ?
The smallest prime factor of $f(54)$ has probably more than $25$ digits.
Can it be proven that $f(n)$ is composite for every integer $n>2$ by finding a forced factor ? $f(n)$ is prime for $n=2$ and no other integer $n\le 700$ ?
Update :
- $P33 = 107407032520007517281843885218879$ divides $F(54)$
- $P28 = 1731761941976002747853061853$ divides $F(94)$
Any ideas ?