21256015321 has 4 divisors (see below), whose sum is σ = 21256456500. Its totient is φ = 21255574144.

The previous prime is 21256015309. The next prime is 21256015349. The reversal of 21256015321 is 12351065212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 16066830025 + 5189185296 = 126755^2 + 72036^2 .

It is a cyclic number.

It is not a de Polignac number, because 21256015321 - 2⁵ = 21256015289 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 21256015321.

It is not an unprimeable number, because it can be changed into a prime (21256015021) 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, 138016 + ... + 248113.

It is an arithmetic number, because the mean of its divisors is an integer number (5314114125).

Almost surely, 2^21256015321 is an apocalyptic number.

It is an amenable number.

21256015321 is a deficient number, since it is larger than the sum of its proper divisors (441179).

21256015321 is an equidigital number, since it uses as much as digits as its factorization.

21256015321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 441178.

The product of its (nonzero) digits is 3600, while the sum is 28.

The spelling of 21256015321 in words is "twenty-one billion, two hundred fifty-six million, fifteen thousand, three hundred twenty-one".