Usually you'd pass the options via a query string, like this:
From an SEO standpoint, query strings represent options for changing how the data is displayed (eg. the order or number of items in a results list), where as in a URL like the example you gave, any change in the URL is considered a separate page (and should have different content). This:
http://www.mywebsite.com/b:5,7,9,/c:5,7,9,/ would be considered a different page to this:
As for the readability, that could be improved by changing the name of your variables. Going back to the list results page example, you might have something like this:
here all the query string variables are logically named, and it's easy to take a guess at what results the page is going to show me.