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A074778
Numbers k such that 2^k+1 and F(k) are not relatively prime, where F(k) denotes the k-th Fibonacci number.
1
10, 14, 30, 36, 42, 50, 54, 70, 74, 90, 98, 100, 108, 110, 114, 126, 130, 134, 150, 154, 162, 170, 174, 178, 180, 182, 190, 192, 194, 202, 210, 222, 230, 238, 250, 252, 254, 266, 270, 290, 294, 300, 310, 322, 324, 330, 340, 342, 350, 352, 354, 370, 378, 390
OFFSET
1,1
COMMENTS
If n is in the sequence, then so is k*n for all odd k. - Robert Israel, Jan 10 2018
LINKS
FORMULA
a(n) seems to be asymptotic to c*n with c=5.8...
MAPLE
N:= 100:
R:= NULL:
count:= 0:
for n from 1 while count < N do
if igcd(2^n+1, combinat:-fibonacci(n)) > 1 then
count:= count+1;
R:= R, n
fi
od:
R; # Robert Israel, Jan 10 2018
MATHEMATICA
Select[Range[400], !CoprimeQ[2^# + 1, Fibonacci[#]] &] (* Amiram Eldar, May 20 2022 *)
PROG
(PARI) isok(n) = gcd(2^n+1, fibonacci(n)) != 1; \\ Michel Marcus, Jan 10 2018
CROSSREFS
Sequence in context: A176810 A377423 A115603 * A162899 A115391 A241162
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Sep 07 2002
STATUS
approved