21028393821 has 4 divisors (see below), whose sum is σ = 28037858432. Its totient is φ = 14018929212.

The previous prime is 21028393807. The next prime is 21028393847. The reversal of 21028393821 is 12839382012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21028393821 - 2¹¹ = 21028391773 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21028393821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21028395821) 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, 3504732301 + ... + 3504732306.

It is an arithmetic number, because the mean of its divisors is an integer number (7009464608).

Almost surely, 2^21028393821 is an apocalyptic number.

It is an amenable number.

21028393821 is a deficient number, since it is larger than the sum of its proper divisors (7009464611).

21028393821 is an equidigital number, since it uses as much as digits as its factorization.

21028393821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7009464610.

The product of its (nonzero) digits is 41472, while the sum is 39.

The spelling of 21028393821 in words is "twenty-one billion, twenty-eight million, three hundred ninety-three thousand, eight hundred twenty-one".