Math students will recognize the number on Dutch mathematician Ludolph van Ceulen's grave as pi -- the mathematical constant used to calculate the ratio of a circle's circumference to its diameter. Van Ceulen, who died from unknown causes in 1610 at age 70, was the first to calculate the value of pi to 35 digits. He was so proud of this achievement that he asked that the number be engraved on his tombstone. Since Van Ceulen's death, pi's value has multiplied exponentially. In 2002, a team of mathematicians at the University of Tokyo took pi to its longest calculation to date -- 1.2 billion numbers. Just try fitting that on their tombstones.