391981879 has 2 divisors, whose sum is σ = 391981880. Its totient is φ = 391981878.

The previous prime is 391981871. The next prime is 391981901. The reversal of 391981879 is 978189193.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 391981879 - 2³ = 391981871 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (391981871) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195990939 + 195990940.

It is an arithmetic number, because the mean of its divisors is an integer number (195990940).

Almost surely, 2^391981879 is an apocalyptic number.

391981879 is a deficient number, since it is larger than the sum of its proper divisors (1).

391981879 is an equidigital number, since it uses as much as digits as its factorization.

391981879 is an evil number, because the sum of its binary digits is even.

The product of its digits is 979776, while the sum is 55.

The square root of 391981879 is about 19798.5322435781. The cubic root of 391981879 is about 731.8498645725.

The spelling of 391981879 in words is "three hundred ninety-one million, nine hundred eighty-one thousand, eight hundred seventy-nine".