18991728 has 120 divisors (see below), whose sum is σ = 61746048. Its totient is φ = 5337216.

The previous prime is 18991711. The next prime is 18991729. The reversal of 18991728 is 82719981.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18991729) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 83551 + ... + 83777.

Almost surely, 2^18991728 is an apocalyptic number.

18991728 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 18991728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30873024).

18991728 is an abundant number, since it is smaller than the sum of its proper divisors (42754320).

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

18991728 is a wasteful number, since it uses less digits than its factorization.

18991728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 331 (or 322 counting only the distinct ones).

The product of its digits is 72576, while the sum is 45.

The square root of 18991728 is about 4357.9499767666. The cubic root of 18991728 is about 266.8014346573.

The spelling of 18991728 in words is "eighteen million, nine hundred ninety-one thousand, seven hundred twenty-eight".