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)=(n-1)*(a(n-1)+a(n-2)) for a(2)=1 and a(1)=0
a(n)=(n-1)*(a(n-1)+a(n-2)) for a(2)=1 and a(1)=0
Natural Language
Math Input
Extended Keyboard
Examples
Upload
Random
