MHB How Does 1/89 Relate to Fibonacci Numbers in Its Decimal Expansion?

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The decimal expansion of 1/89 is 0.01123595, which aligns with the Fibonacci sequence, where each digit corresponds to a Fibonacci number. The relationship can be expressed mathematically as the sum of Fibonacci numbers divided by powers of ten, specifically, 1/10 times the sum of Fibonacci numbers equals 1/89. This connection is derived from the generating function of Fibonacci numbers, which is g(x) = x / (1 - x - x^2). By substituting x = 1/10 into this function, the series converges to 10/89. The discussion invites further exploration and proof of this elegant mathematical relationship.
soroban
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\text{We have: }\:\dfrac{1}{89} \;=\;0.01123595\,\,.\,.\,.


\text{The decimal is formed like this:}

. . 0.0{\bf1}
. . 0.00{\bf1}
. . 0.000{\bf2}
. . 0.0000{\bf3}
. . 0.00000{\bf5}
. . 0.000000{\bf8}
. . 0.000000{\bf{13}}
. . 0.0000000{\bf{21}}
. . 0.00000000{\bf{34}}
. . . . . . \vdots


\displaystyle\text{It seems that: }\:\frac{1}{10}\sum^{\infty}_{n=1} \frac{F_n}{10^n} \;=\;\frac{1}{89}

. . \text{where }F_n\text{ is the }n^{th}\text{ Fibonacci number.}


\text{Care to prove it?}
 
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soroban said:
\text{We have: }\:\dfrac{1}{89} \;=\;0.01123595\,\,.\,.\,.


\text{The decimal is formed like this:}. . 0.0{\bf1}
. . 0.00{\bf1}
. . 0.000{\bf2}
. . 0.0000{\bf3}
. . 0.00000{\bf5}
. . 0.000000{\bf8}
. . 0.000000{\bf{13}}
. . 0.0000000{\bf{21}}
. . 0.00000000{\bf{34}}
. . . . . . \vdots


\displaystyle\text{It seems that: }\:\frac{1}{10}\sum^{\infty}_{n=1} \frac{F_n}{10^n} \;=\;\frac{1}{89}

. . \text{where }F_n\text{ is the }n^{th}\text{ Fibonacci number.}


\text{Care to prove it?}

The Fibonacci's numbers have been studied for something like 800 years and, among the others 'discoveries' there is the the generating function that can be directly derived from the difference equation $\displaystyle f_{n+2}= f_{n+1}+f_{n},\ f_{0}=0,\ f_{1}=1$...

$\displaystyle g(x)=\sum_{n=1}^{\infty} f_{n}\ x^{n} = \frac{x}{1-x-x^{2}}$ (1)

Setting in (1) $x=\frac{1}{10}$ You have...

$\displaystyle \sum_{n=1}^{\infty} f_{n}\ 10^{- n} = \frac{10}{89}$ (2)

Kind regards

$\chi$ $\sigma$
 
chisigma said:
The Fibonacci's numbers have been studied for something like 800 years and, among the others 'discoveries' there is the the generating function that can be directly derived from the difference equation $\displaystyle f_{n+2}= f_{n+1}+f_{n},\ f_{0}=0,\ f_{1}=1$...

$\displaystyle g(x)=\sum_{n=1}^{\infty} f_{n}\ x^{n} = \frac{x}{1-x-x^{2}}$ (1)

Setting in (1) $x=\frac{1}{10}$ You have...

$\displaystyle \sum_{n=1}^{\infty} f_{n}\ 10^{- n} = \frac{10}{89}$ (2)

... but much more 'elegant' is what You obtain setting in (1) $x=\frac{1}{2}$...

$\displaystyle \sum_{n=1}^{\infty} \frac{f_{n}}{2^{n}} = 2$

Not bad!(Happy)...

Kind regards

$\chi$ $\sigma$
 
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