I'll be posting my Wolfram|Alpha widgets here.
Here's my first one for calculating sequences:
This one also graphs sequences and computes series total:
The Wolfram Alpha Team did an excellent job with their widget builder. If you want to see the "source code" for the widgets you'll need to first sign up for a Wolfram Alpha developer account (very easy), then choose the "Customize Widget" option at the W|A page for the sequences widget or the W|A page for the sequences and series widget
