21000020021 has 8 divisors (see below), whose sum is σ = 21075775104. Its totient is φ = 20924366400.

The previous prime is 21000019991. The next prime is 21000020053. The reversal of 21000020021 is 12002000012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21000020021 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21000019990 and 21000020008.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000020221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 402221 + ... + 451421.

It is an arithmetic number, because the mean of its divisors is an integer number (2634471888).

Almost surely, 2^21000020021 is an apocalyptic number.

It is an amenable number.

21000020021 is a deficient number, since it is larger than the sum of its proper divisors (75755083).

21000020021 is a wasteful number, since it uses less digits than its factorization.

21000020021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50731.

The product of its (nonzero) digits is 8, while the sum is 8.

Adding to 21000020021 its reverse (12002000012), we get a palindrome (33002020033).

The spelling of 21000020021 in words is "twenty-one billion, twenty thousand, twenty-one".