391191981 has 16 divisors (see below), whose sum is σ = 576284544. Its totient is φ = 234781184.

The previous prime is 391191967. The next prime is 391192001. The reversal of 391191981 is 189191193.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 391191981 - 2⁶ = 391191917 is a prime.

It is a super-2 number, since 2×391191981² = 306062331997408722, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (391141981) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 165576 + ... + 167921.

It is an arithmetic number, because the mean of its divisors is an integer number (36017784).

Almost surely, 2^391191981 is an apocalyptic number.

It is an amenable number.

391191981 is a deficient number, since it is larger than the sum of its proper divisors (185092563).

391191981 is a wasteful number, since it uses less digits than its factorization.

391191981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 333540.

The product of its digits is 17496, while the sum is 42.

The square root of 391191981 is about 19778.5737857915. The cubic root of 391191981 is about 731.3579409072.

The spelling of 391191981 in words is "three hundred ninety-one million, one hundred ninety-one thousand, nine hundred eighty-one".