391405991 has 2 divisors, whose sum is σ = 391405992. Its totient is φ = 391405990.

The previous prime is 391405981. The next prime is 391406021. The reversal of 391405991 is 199504193.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 391405991 - 2¹⁸ = 391143847 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (391405981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195702995 + 195702996.

It is an arithmetic number, because the mean of its divisors is an integer number (195702996).

Almost surely, 2^391405991 is an apocalyptic number.

391405991 is a deficient number, since it is larger than the sum of its proper divisors (1).

391405991 is an equidigital number, since it uses as much as digits as its factorization.

391405991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 43740, while the sum is 41.

The square root of 391405991 is about 19783.9831934826. The cubic root of 391405991 is about 731.4912849659.

The spelling of 391405991 in words is "three hundred ninety-one million, four hundred five thousand, nine hundred ninety-one".