21566016321 has 4 divisors (see below), whose sum is σ = 28754688432. Its totient is φ = 14377344212.

The previous prime is 21566016293. The next prime is 21566016331. The reversal of 21566016321 is 12361066512.

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 21566016321 - 2⁷ = 21566016193 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21566016331) 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, 3594336051 + ... + 3594336056.

It is an arithmetic number, because the mean of its divisors is an integer number (7188672108).

Almost surely, 2^21566016321 is an apocalyptic number.

It is an amenable number.

21566016321 is a deficient number, since it is larger than the sum of its proper divisors (7188672111).

21566016321 is an equidigital number, since it uses as much as digits as its factorization.

21566016321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7188672110.

The product of its (nonzero) digits is 12960, while the sum is 33.

The spelling of 21566016321 in words is "twenty-one billion, five hundred sixty-six million, sixteen thousand, three hundred twenty-one".