Fermat's Last Theorem
To prove the Fermat's Last Theorem for a strong irregular prime "p" is more difficult (since Kummer proved the first case of Fermat's Last Theorem for B-regular primes, Vandiver proved the first case of Fermat's Last Theorem for E-regular primes), the most difficult is that "p" is not only a strong irregular prime, but , , , , , and are also all composite (Legendre proved the first case of Fermat's Last Theorem for primes "p" such that at least one of , , , , , and is prime), the first few such "p" are