I don't remember a lot of Carl Sagan's novel "Contact," but there was a bit that was really cool and imaginative.

From Wikipedia:

In a kind of postscript, Ellie, acting upon a suggestion by the senders of the Message, works on a program which computes the digits of pi to record lengths and in different bases. Very, very far from the decimal point (10^20) and in base 11, it finds that a special pattern does exist when the numbers stop varying randomly and start producing 1's and 0's in a very long string. The string's length is the product of 11 prime numbers. The 1's and 0's when organized as a square of specific dimensions form a perfect circle.

While looking up the reference, I found this page, which looks like a very interesting browsing experience.