OFFSET
1,4
COMMENTS
The frequencies seem interesting. In the early terms, 5 appears notably rarely, i.e., not until at a(240), whereas several other numbers appear notably frequently, e.g., 24 appears 13 times before a(240). - Peter Munn, May 03 2023
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..448
FORMULA
EXAMPLE
For n=4, Fibonacci(4)=3 and 3*Fibonacci(k)+1 is not prime until k reaches 3, so a(4)=3.
MATHEMATICA
Table[m = Fibonacci[n]; k = 1; While[! PrimeQ[m*Fibonacci[k] + 1], k++]; k, {n, 120}] (* Michael De Vlieger, May 03 2023 *)
PROG
(PARI) a(n) = my(F=fibonacci(n), k=1); while (!ispseudoprime(F*fibonacci(k) + 1), k++); k; \\ Michel Marcus, Apr 18 2023
(Python)
from itertools import count
from sympy import fibonacci, isprime
def A362376(n):
a = b = fibonacci(n)
for k in count(1):
if isprime(a+1):
return k
a, b = b, a+b # Chai Wah Wu, May 03 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Jack Braxton, Apr 17 2023
EXTENSIONS
More terms from Michel Marcus, Apr 18 2023
STATUS
approved