391997 has 4 divisors (see below), whose sum is σ = 395580. Its totient is φ = 388416.

The previous prime is 391987. The next prime is 391999. The reversal of 391997 is 799193.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 799193 = 401 ⋅1993.

It can be written as a sum of positive squares in 2 ways, for example, as 8836 + 383161 = 94^2 + 619^2 .

It is a cyclic number.

It is not a de Polignac number, because 391997 - 2¹⁸ = 129853 is a prime.

It is a Duffinian number.

It is a plaindrome in base 6.

It is a self number, because there is not a number n which added to its sum of digits gives 391997.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (391999) 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, 1622 + ... + 1847.

It is an arithmetic number, because the mean of its divisors is an integer number (98895).

2³⁹¹⁹⁹⁷ is an apocalyptic number.

It is an amenable number.

391997 is a deficient number, since it is larger than the sum of its proper divisors (3583).

391997 is a wasteful number, since it uses less digits than its factorization.

391997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3582.

The product of its digits is 15309, while the sum is 38.

The square root of 391997 is about 626.0966379082. The cubic root of 391997 is about 73.1859275007.

The spelling of 391997 in words is "three hundred ninety-one thousand, nine hundred ninety-seven".