391999 has 2 divisors, whose sum is σ = 392000. Its totient is φ = 391998.

The previous prime is 391987. The next prime is 392011. The reversal of 391999 is 999193.

It is a balanced prime because it is at equal distance from previous prime (391987) and next prime (392011).

It is a cyclic number.

It is not a de Polignac number, because 391999 - 2⁵ = 391967 is a prime.

391999 is a modest number, since divided by 999 gives 391 as remainder.

391999 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (391939) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195999 + 196000.

It is an arithmetic number, because the mean of its divisors is an integer number (196000).

2³⁹¹⁹⁹⁹ is an apocalyptic number.

391999 is a deficient number, since it is larger than the sum of its proper divisors (1).

391999 is an equidigital number, since it uses as much as digits as its factorization.

391999 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 19683, while the sum is 40.

The square root of 391999 is about 626.0982351037. The cubic root of 391999 is about 73.1860519673.

The spelling of 391999 in words is "three hundred ninety-one thousand, nine hundred ninety-nine".