OFFSET
1,3
FORMULA
a(n) = 1 + floor( log_2( A000045(n) ) ).
MATHEMATICA
f[n_] := 1 + Floor@ Log2@ Fibonacci@ n; Array[f, 74] (* Robert G. Wilson v, Jun 24 2011 *)
IntegerLength[#, 2]&/@Fibonacci[Range[80]] (* Harvey P. Dale, Feb 11 2015 *)
PROG
(PARI) a(n)={
if(n<99, return(#binary(fibonacci(n))));
localbitprec(logint(n*6351109\9148265, 2)+64);
my(s=sqrt(5), phi=(s+1)/2, x=n*log(phi)-log(s));
ceil(x/log(2));
} \\ Charles R Greathouse IV, Aug 24 2021
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
EXTENSIONS
More terms from James A. Sellers
STATUS
approved