20391728 has 40 divisors (see below), whose sum is σ = 45642912. Its totient is φ = 8644608.

The previous prime is 20391713. The next prime is 20391737. The reversal of 20391728 is 82719302.

It is a junction number, because it is equal to n+sod(n) for n = 20391694 and 20391703.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9926 + ... + 11802.

Almost surely, 2^20391728 is an apocalyptic number.

20391728 is a gapful number since it is divisible by the number (28) 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 20391728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22821456).

20391728 is an abundant number, since it is smaller than the sum of its proper divisors (25251184).

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

20391728 is a wasteful number, since it uses less digits than its factorization.

20391728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1989 (or 1983 counting only the distinct ones).

The product of its (nonzero) digits is 6048, while the sum is 32.

The square root of 20391728 is about 4515.7200976146. The cubic root of 20391728 is about 273.2025046449.

The spelling of 20391728 in words is "twenty million, three hundred ninety-one thousand, seven hundred twenty-eight".