OFFSET
0,1
COMMENTS
LINKS
Pontus von Brömssen, Table of n, a(n) for n = 0..7122
Robert Gerbicz, Re: Add a Fibonacci number to get a prime, SeqFan mailing list, March 28, 2023.
FORMULA
a(n) = 0 if and only if n is prime.
a(n) = -1 if n == 14475 (mod m), where m = 2*3*5*7*11*23*31 = 1647030 (see Gerbicz link).
EXAMPLE
The first Fibonacci number F such that 25+F is prime is F = 34 = A000045(9), so a(25) = 9.
MATHEMATICA
a[n_] := Module[{k = 0}, While[! PrimeQ[n + Fibonacci[k]], k++]; k]; Array[a, 100, 0] (* Amiram Eldar, Mar 30 2023 *)
PROG
(Python)
from sympy import isprime, fibonacci
from itertools import count
def A361902(n):
# Note: the function hangs if a(n) = -1.
return next(k for k in count() if isprime(n+fibonacci(k)))
(PARI) a(n) = my(k=0); while (!isprime(n+fibonacci(k)), k++); k; \\ Michel Marcus, Mar 30 2023
CROSSREFS
KEYWORD
sign
AUTHOR
Pontus von Brömssen, Mar 28 2023
STATUS
approved