21536640221 has 4 divisors (see below), whose sum is σ = 21809256000. Its totient is φ = 21264024444.

The previous prime is 21536640211. The next prime is 21536640253. The reversal of 21536640221 is 12204663512.

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 21536640221 - 2²⁶ = 21469531357 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 (21536640211) 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, 136307771 + ... + 136307928.

It is an arithmetic number, because the mean of its divisors is an integer number (5452314000).

Almost surely, 2^21536640221 is an apocalyptic number.

It is an amenable number.

21536640221 is a deficient number, since it is larger than the sum of its proper divisors (272615779).

21536640221 is an equidigital number, since it uses as much as digits as its factorization.

21536640221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 272615778.

The product of its (nonzero) digits is 17280, while the sum is 32.

The spelling of 21536640221 in words is "twenty-one billion, five hundred thirty-six million, six hundred forty thousand, two hundred twenty-one".