21047495657 has 4 divisors (see below), whose sum is σ = 21048285396. Its totient is φ = 21046705920.

The previous prime is 21047495647. The next prime is 21047495659. The reversal of 21047495657 is 75659474012.

It is a happy number.

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 7799715856 + 13247779801 = 88316^2 + 115099^2 .

It is a cyclic number.

It is not a de Polignac number, because 21047495657 - 2⁴ = 21047495641 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21047495659) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 353444 + ... + 408677.

It is an arithmetic number, because the mean of its divisors is an integer number (5262071349).

Almost surely, 2^21047495657 is an apocalyptic number.

It is an amenable number.

21047495657 is a deficient number, since it is larger than the sum of its proper divisors (789739).

21047495657 is an equidigital number, since it uses as much as digits as its factorization.

21047495657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 789738.

The product of its (nonzero) digits is 2116800, while the sum is 50.

The spelling of 21047495657 in words is "twenty-one billion, forty-seven million, four hundred ninety-five thousand, six hundred fifty-seven".