 (<em>R<sub>*</sub></em>), of which one fifth (<em>f<sub>p</sub></em>) have about 3 planets (<em>n<sub>e</sub></em>), of which 100% (<em>f<sub>l</sub></em>) will eventually develop life, of which 100% (<em>f<sub>i</sub></em>) will eventually become intelligent, of which 10% (<em>f<sub>c</sub></em>) will be able to communicate, and will last 1 million years (<em>L</em>).</p>
    <p>If you put all these numbers together, you'll get to the number 60,000. There should be 60 thousand civilization at any one time