What a fun course this was. The lecturer of Introduction to Number Theory, Ed Burger, a math PhD, looks like what one would expect a mathematician to look like: thin, tall, geeky looking, wearing a rather bland costume, but with a colorful tie, curly hair and large glasses, with a sincere smile that seems a bit sad. The thing is, he is also a lot of fun and his enthusiasm regarding mathematics is not only obvious, but catchy as well.
The course itself requires very little if any mathematical education to understand, being mostly about ideas, rather than formulas. It is a Teaching Company course, and each lecture builds upon the understanding from the previous ones, making surprising and really fun connections.
I was very sad when the course ended, I wanted more! Happily, I've got "The Joy of Thinking" and "Zero to Infinity - a History of Numbers" that are also lectured by Ed Burger and I can't wait to watch them all. I highly recommend the course, even if one is not interested in math. It opens the mind on a way of thinking, useful in any situation, rather than anything specific.