391998 has 16 divisors (see below), whose sum is σ = 794880. Its totient is φ = 128856.

The previous prime is 391987. The next prime is 391999. The reversal of 391998 is 899193.

391998 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 391998.

It is not an unprimeable number, because it can be changed into a prime (391999) by changing a digit.

391998 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 61 + ... + 887.

It is an arithmetic number, because the mean of its divisors is an integer number (49680).

2³⁹¹⁹⁹⁸ is an apocalyptic number.

391998 is an abundant number, since it is smaller than the sum of its proper divisors (402882).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

391998 is a wasteful number, since it uses less digits than its factorization.

391998 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 911.

The product of its digits is 17496, while the sum is 39.

The square root of 391998 is about 626.0974365065. The cubic root of 391998 is about 73.1859897341.

The spelling of 391998 in words is "three hundred ninety-one thousand, nine hundred ninety-eight".