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I am not divisible by anything, but there's a formula to find my value.

I have a 9 in the ten-billionths place.

Multiply me by $d$ to get $c$.

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The answer is

$\pi$


Multiply me by $d$ to get $c$.

Pi times the diameter of a circle is the circumference.

I have a 9 in the ten-billionths place.

Pi's decimal value is 3.141592653589...

there's a formula to solve my value.

There are a number of continued fractions that evaluate to $\pi$.

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