You can put this solution on YOUR website!
These look like Jacobsthal numbers, except that that sequence starts with 0, 1, 1, 3, 5, 11, ...
This sequence is similar to the Fibonacci sequence. Each number is the sequence is found by adding the number preceding it to twice the number before that.
For example, in your sequence
11 is 5 plus two times 3.
21 is 11 plus two times 5.
Here's a wikipedia link: http://en.wikipedia.org/wiki/Jacobsthal_number
You can also google Jacobsthal numbers and find all sorts of cool stuff. Hope this helps.