Exhausted, he called on his last ounce of strength.

I had to work all the harder with two people off sick.

Fermat's little theorem says that if n is prime and gcd(a,n) = 1, then aⁿ⁻¹ ≡ 1 (mod n), so it follows that n must be composite, even though we have not produced a factor.

A gentle breeze fills the huge sail of our dhow, and draws us through the water that ripples musically against her sides.