<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> In the 18th century, Johann Heinrich Lambert proved that the number π (pi) is irrational: that is, it cannot be expressed as a fraction a / b, where a is an integer and b is a non-zero integer . In the 19th century, Charles Hermite found a proof that requires no prerequisite knowledge beyond basic calculus . Three simplifications of Hermite's proof are due to Mary Cartwright, Ivan Niven, and Nicolas Bourbaki . Another proof, which is a simplification of Lambert's proof, is due to Miklós Laczkovich . </P> <P> In 1882, Ferdinand von Lindemann proved that π is not just irrational, but transcendental as well . </P>

What does it mean that pi is an irrational number
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