391971391 has 4 divisors (see below), whose sum is σ = 447967312. Its totient is φ = 335975472.

The previous prime is 391971367. The next prime is 391971427. The reversal of 391971391 is 193179193.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 391971391 - 2⁷ = 391971263 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (391971361) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27997950 + ... + 27997963.

It is an arithmetic number, because the mean of its divisors is an integer number (111991828).

Almost surely, 2^391971391 is an apocalyptic number.

391971391 is a deficient number, since it is larger than the sum of its proper divisors (55995921).

391971391 is an equidigital number, since it uses as much as digits as its factorization.

391971391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55995920.

The product of its digits is 45927, while the sum is 43.

The square root of 391971391 is about 19798.2673736870. The cubic root of 391971391 is about 731.8433373066.

The spelling of 391971391 in words is "three hundred ninety-one million, nine hundred seventy-one thousand, three hundred ninety-one".