400391 has 2 divisors, whose sum is σ = 400392. Its totient is φ = 400390.

The previous prime is 400381. The next prime is 400409. The reversal of 400391 is 193004.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 400391 - 2¹⁸ = 138247 is a prime.

It is a Sophie Germain prime.

It is a zygodrome in base 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (400321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 200195 + 200196.

It is an arithmetic number, because the mean of its divisors is an integer number (200196).

2⁴⁰⁰³⁹¹ is an apocalyptic number.

400391 is a deficient number, since it is larger than the sum of its proper divisors (1).

400391 is an equidigital number, since it uses as much as digits as its factorization.

400391 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 108, while the sum is 17.

The square root of 400391 is about 632.7645691725. The cubic root of 400391 is about 73.7046297598.

Adding to 400391 its reverse (193004), we get a palindrome (593395).

The spelling of 400391 in words is "four hundred thousand, three hundred ninety-one".