4391 is a prime number. It is a Sophie Germain prime because 2 x 4391 + 1 = 8783 is also a prime.
4391 is the smaller of two consecutive Sophie Germain primes with the same digital sum (A118506).
4391 is the sum of the first 47 primes minus 47 (A101301).
4391 is a number that cannot be written as a sum of three squares.
4391 is 3332 in base 11 (A032811).