20728321 has 4 divisors (see below), whose sum is σ = 21947652. Its totient is φ = 19508992.

The previous prime is 20728291. The next prime is 20728339. The reversal of 20728321 is 12382702.

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

It can be written as a sum of positive squares in 2 ways, for example, as 19009600 + 1718721 = 4360^2 + 1311^2 .

It is a cyclic number.

It is not a de Polignac number, because 20728321 - 2⁵ = 20728289 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20728121) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 609640 + ... + 609673.

It is an arithmetic number, because the mean of its divisors is an integer number (5486913).

Almost surely, 2^20728321 is an apocalyptic number.

It is an amenable number.

20728321 is a deficient number, since it is larger than the sum of its proper divisors (1219331).

20728321 is a wasteful number, since it uses less digits than its factorization.

20728321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1219330.

The product of its (nonzero) digits is 1344, while the sum is 25.

The square root of 20728321 is about 4552.8365883260. The cubic root of 20728321 is about 274.6975009830.

The spelling of 20728321 in words is "twenty million, seven hundred twenty-eight thousand, three hundred twenty-one".