how can I display the first post in a single column and others in columns?

I currently have all the posts displayed in one column:

1
2
3
…

I’d like to achieve something similar:

1
23
4
56
…

does anyone have any ideas of how I could do this? is it possible?
thank you so much in advance 🙂

[closed as duplicate – continue with http://wordpress.org/support/topic/add-a-class-to-every-second-and-third-post?replies=2 ]