18351991 has 8 divisors (see below), whose sum is σ = 21160224. Its totient is φ = 15590400.

The previous prime is 18351989. The next prime is 18352001. The reversal of 18351991 is 19915381.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 18351991 - 2¹ = 18351989 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18351991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18351901) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10810 + ... + 12391.

It is an arithmetic number, because the mean of its divisors is an integer number (2645028).

Almost surely, 2^18351991 is an apocalyptic number.

18351991 is a deficient number, since it is larger than the sum of its proper divisors (2808233).

18351991 is a wasteful number, since it uses less digits than its factorization.

18351991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23321.

The product of its digits is 9720, while the sum is 37.

The square root of 18351991 is about 4283.9223849178. The cubic root of 18351991 is about 263.7714150458.

The spelling of 18351991 in words is "eighteen million, three hundred fifty-one thousand, nine hundred ninety-one".