21056516021 has 4 divisors (see below), whose sum is σ = 21057557472. Its totient is φ = 21055474572.

The previous prime is 21056516003. The next prime is 21056516023. The reversal of 21056516021 is 12061565012.

It is a happy number.

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 a cyclic number.

It is not a de Polignac number, because 21056516021 - 2⁶ = 21056515957 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 (21056516023) 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, 489785 + ... + 531038.

It is an arithmetic number, because the mean of its divisors is an integer number (5264389368).

Almost surely, 2^21056516021 is an apocalyptic number.

It is an amenable number.

21056516021 is a deficient number, since it is larger than the sum of its proper divisors (1041451).

21056516021 is a wasteful number, since it uses less digits than its factorization.

21056516021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1041450.

The product of its (nonzero) digits is 3600, while the sum is 29.

The spelling of 21056516021 in words is "twenty-one billion, fifty-six million, five hundred sixteen thousand, twenty-one".