| Thus, Fermat's theorem gives a test that is necessary but not sufficient for primality. |
| That is because quick and dirty techniques for testing primality already exist. |
| However, if Dr Agrawal's primality test can be extended to factoring numbers, it would mean a rejigging of modern cryptography. |
| In 1876 the French mathematician Édouard Lucas found a way to test the primality of Mersenne numbers. |
| Instead, mathematicians turn to other, indirect, methods that can test for primality without factorisation. |
| So-called primality testing plays a crucial role in the widely used RSA algorithm, whose security relies on the difficulty of finding a number's prime factors. |
