Lucas is known for his study of the Fibonacci numbers, including a formula for finding the nth term of the sequence. The related Lucas sequence is named after him. He devised a new method for testing the primality of numbers that did not require finding all of their factors. In 1930, Derrick Henry Lehmer expanded on this work to create the Lucas-Lehmer test. In 1876, Lucas proved the primality of $\displaystyle{ 2^{127}{-}1 }$ (M12) and this remained the highest Mersenne prime for almost 75 years, and is still the highest prime number discovered without the aid of a computer.