20000021 has 4 divisors (see below), whose sum is σ = 20086092. Its totient is φ = 19913952.

The previous prime is 20000003. The next prime is 20000023. The reversal of 20000021 is 12000002.

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 12327121 + 7672900 = 3511^2 + 2770^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20000021 is a prime.

It is a Duffinian number.

20000021 is a modest number, since divided by 21 gives 20 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20000023) 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, 42686 + ... + 43151.

It is an arithmetic number, because the mean of its divisors is an integer number (5021523).

Almost surely, 2^20000021 is an apocalyptic number.

It is an amenable number.

20000021 is a deficient number, since it is larger than the sum of its proper divisors (86071).

20000021 is an equidigital number, since it uses as much as digits as its factorization.

20000021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 86070.

The product of its (nonzero) digits is 4, while the sum is 5.

The square root of 20000021 is about 4472.1383028703. The cubic root of 20000021 is about 271.4418566641.

Adding to 20000021 its reverse (12000002), we get a palindrome (32000023).

Multiplying 20000021 by its reverse (12000002), we get a palindrome (240000292000042).

The spelling of 20000021 in words is "twenty million, twenty-one", and thus it is an aban number and an uban number.