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.
a(n)=2a(n-1)-a(n-2)+n, a(0)=0, a(1)=2/3
Natural Language
Math Input
Extended Keyboard
Examples
Upload
Random