21056605357 has 4 divisors (see below), whose sum is σ = 21057046236. Its totient is φ = 21056164480.

The previous prime is 21056605333. The next prime is 21056605417. The reversal of 21056605357 is 75350665012.

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 2291441161 + 18765164196 = 47869^2 + 136986^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21056605357 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 (21056605057) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 138694 + ... + 247687.

It is an arithmetic number, because the mean of its divisors is an integer number (5264261559).

Almost surely, 2^21056605357 is an apocalyptic number.

It is an amenable number.

21056605357 is a deficient number, since it is larger than the sum of its proper divisors (440879).

21056605357 is an equidigital number, since it uses as much as digits as its factorization.

21056605357 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 440878.

The product of its (nonzero) digits is 189000, while the sum is 40.

The spelling of 21056605357 in words is "twenty-one billion, fifty-six million, six hundred five thousand, three hundred fifty-seven".