Agrawal's conjecture that given coprime positive integers n and r, if (X

1)^n \equiv X^n - 1 \pmod{n, X^r - 1}, then either n is prime or n^{2} \equiv 1 \pmod{r}

Open the “Prime numbers” section on Wikipedia →

Source: List of unsolved problems in mathematics (CC BY-SA 4.0)