Uh oh! Wolfram|Alpha doesn't run without JavaScript.
Please enable JavaScript. If you don't know how, you can find instructions
here
.
Once you've done that, refresh this page to start using Wolfram|Alpha.
\sum_{n=1}^infty ((n-1)\cdot 2^{n-2}\cdot 7+2^{n-1})\cdot \frac1{3^{n}}
Natural Language
Math Input
Extended Keyboard
Examples
Upload
Random