20439821 has 4 divisors (see below), whose sum is σ = 20825532. Its totient is φ = 20054112.

The previous prime is 20439803. The next prime is 20439841. The reversal of 20439821 is 12893402.

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 18826921 + 1612900 = 4339^2 + 1270^2 .

It is a cyclic number.

It is not a de Polignac number, because 20439821 - 2²² = 16245517 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20439841) 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, 192776 + ... + 192881.

It is an arithmetic number, because the mean of its divisors is an integer number (5206383).

Almost surely, 2^20439821 is an apocalyptic number.

It is an amenable number.

20439821 is a deficient number, since it is larger than the sum of its proper divisors (385711).

20439821 is an equidigital number, since it uses as much as digits as its factorization.

20439821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 385710.

The product of its (nonzero) digits is 3456, while the sum is 29.

The square root of 20439821 is about 4521.0420259051. The cubic root of 20439821 is about 273.4171147426.

The spelling of 20439821 in words is "twenty million, four hundred thirty-nine thousand, eight hundred twenty-one".