18423991 has 4 divisors (see below), whose sum is σ = 18484312. Its totient is φ = 18363672.

The previous prime is 18423967. The next prime is 18424027. The reversal of 18423991 is 19932481.

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

It is a cyclic number.

It is not a de Polignac number, because 18423991 - 2¹¹ = 18421943 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 18423991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18423931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 29700 + ... + 30313.

It is an arithmetic number, because the mean of its divisors is an integer number (4621078).

Almost surely, 2^18423991 is an apocalyptic number.

18423991 is a deficient number, since it is larger than the sum of its proper divisors (60321).

18423991 is an equidigital number, since it uses as much as digits as its factorization.

18423991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 60320.

The product of its digits is 15552, while the sum is 37.

The square root of 18423991 is about 4292.3176723071. The cubic root of 18423991 is about 264.1159146243.

The spelling of 18423991 in words is "eighteen million, four hundred twenty-three thousand, nine hundred ninety-one".