A192044 Decimal approximation of x such that f(x)=r+1, where f is the Fibonacci function described in Comments and r=(golden ratio).

3, 7, 0, 8, 2, 2, 8, 3, 1, 9, 6, 1, 1, 8, 1, 5, 4, 4, 6, 2, 2, 7, 9, 5, 6, 9, 7, 6, 0, 4, 7, 6, 2, 9, 0, 3, 1, 4, 1, 4, 4, 4, 7, 8, 0, 1, 5, 1, 4, 7, 0, 4, 6, 7, 1, 2, 4, 7, 2, 4, 0, 2, 3, 9, 9, 5, 4, 0, 8, 0, 1, 9, 6, 5, 8, 7, 3, 7, 9, 3, 6, 4, 3, 9, 8, 5, 9, 4, 2, 2, 6, 1, 1, 6, 1, 6, 0, 6, 3, 3

Offset: 1

Author

Clark Kimberling, Jun 21 2011

Keywords

• nonn
• cons

Comments

f(x)=(r^x-r^(-x*cos[pi*x]))/sqrt(5), where r=(golden ratio)=(1+sqrt(5))/2. This function, a variant of the Binet formula, gives Fibonacci numbers for integer values of x; e.g., f(3)=2, f(4)=3, f(5)=5.

Examples

			3.70822831961181544622795697604762903141444780151470467124724
		

Crossrefs

Cf. A192038, A104457.

Programs

Mathematica

r = GoldenRatio; s = 1/Sqrt[5];
f[x_] := s (r^x - r^-x Cos[Pi x]);
x /. FindRoot[Fibonacci[x] == r+1, {x, 5}, WorkingPrecision -> 100]
RealDigits[%, 10]
(Show[Plot[#1, #2], ListPlot[Table[{x, #1}, #2]]] &)[
Fibonacci[x], {x, -7, 7}]
(* Peter J. C. Moses, Jun 21 2011 *)