OFFSET
1,18
COMMENTS
See also A375089, which is the main entry.
[This was the version of A375089 that was originally submitted. I think both belong in the OEIS. - N. J. A. Sloane, Aug 28 2024]
FORMULA
a(2n) = A375089(n). - Chai Wah Wu, Aug 28 2024
PROG
(Python)
from functools import lru_cache
from math import gcd, lcm
from sympy import factorint, divisors, fibonacci
def A375519(n):
@lru_cache(maxsize=None)
def A001175(n):
if n == 1:
return 1
f = factorint(n).items()
if len(f) > 1:
return lcm(*(A001175(a**b) for a, b in f))
else:
k, x = 1, (1, 1)
while x != (0, 1):
k += 1
x = (x[1], (x[0]+x[1]) % n)
return k
a, b = fibonacci(n+1), fibonacci(n)
return sum(1 for d in divisors(gcd(a-1, b), generator=True) if A001175(d)==n) # Chai Wah Wu, Aug 28 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Oliver Lippard and Brennan G. Benfield, Jul 29 2024
STATUS
approved