391999987 has 2 divisors, whose sum is σ = 391999988. Its totient is φ = 391999986.

The previous prime is 391999967. The next prime is 392000009. The reversal of 391999987 is 789999193.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 391999987 - 2¹⁹ = 391475699 is a prime.

It is not a weakly prime, because it can be changed into another prime (391999967) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195999993 + 195999994.

It is an arithmetic number, because the mean of its divisors is an integer number (195999994).

Almost surely, 2^391999987 is an apocalyptic number.

391999987 is a deficient number, since it is larger than the sum of its proper divisors (1).

391999987 is an equidigital number, since it uses as much as digits as its factorization.

391999987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9920232, while the sum is 64.

The square root of 391999987 is about 19798.9895449238. The cubic root of 391999987 is about 731.8611339143.

The spelling of 391999987 in words is "three hundred ninety-one million, nine hundred ninety-nine thousand, nine hundred eighty-seven".