François Édouard Anatole Lucas (4 April 1842 – 3 October 1891) was a French mathematician. Lucas is known for his study of the Fibonacci sequence. The related Lucas sequence is named after him. He gave a formula for finding the n^th term of the Fibonacci sequence.

Lucas was educated at the École Normale Supérieure. He worked in the Paris observatory and later became a professor of mathematics in Paris. In the meantime he served in the army.

Lucas posed a challenge to prove that the only solution of the Diophantine equation:

with N > 1 is when N = 24 and M = 70. It was not until 1918 that a proof (using hyperelliptic functions) was found for this remarkable fact, which has relevance to the bosonic string theory in 26 dimensions.

He devised methods for testing the primality of numbers. In 1857, at age 15, Lucas began testing the primality of 2¹²⁷ − 1 by hand, using Lucas Sequences. In 1876, after 19 years of testing, he finally proved that 2¹²⁷ − 1 was prime; this would remain the largest known Mersenne prime for three quarters of a century. This may stand forever as the largest prime number proven by hand. Later Derrick Henry Lehmer refined Lucas' primality tests and obtained the Lucas-Lehmer test.

He worked on the development of the umbral calculus.

Lucas was also interested in recreational mathematics. He found an elegant binary solution to the Baguenaudier puzzle. He more notably invented the Tower of Hanoi puzzle, which he marketed under the nickname N. Claus de Siam, an anagram of Lucas d'Amiens, and published for the first time a description of the Dots and Boxes game in 1889.

Lucas died in unusual circumstances. At the banquet of the annual congress of the Association française pour l'avancement des sciences a waiter dropped some crockery and a piece of broken plate cut Lucas on the cheek. He died a few days later of a severe skin inflammation probably caused by septicemia. Lucas was only 49 years old when he died.