I'm quite fond of the number 10. Nice and even and round and the basis for our entire number system.

Every number is special in its own way, though. I really like this story that GH Hardy tells about Ramanujan, the last great mathematical genius:

I remember once going to see him when he was ill at Putney. I had ridden in taxi cab number 1729 and remarked that the number seemed to me rather a dull one, and that I hoped it was not an unfavorable omen. "No", he replied, "it is a very interesting number; it is the smallest number expressible as the sum of two cubes in two different ways."
The two different ways are
1729 = 13 + 123 = 93 + 103.