21513955857 has 4 divisors (see below), whose sum is σ = 28685274480. Its totient is φ = 14342637236.

The previous prime is 21513955847. The next prime is 21513955867. The reversal of 21513955857 is 75855931512.

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 an interprime number because it is at equal distance from previous prime (21513955847) and next prime (21513955867).

It is a cyclic number.

It is not a de Polignac number, because 21513955857 - 2²⁷ = 21379738129 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21513955807) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3585659307 + ... + 3585659312.

It is an arithmetic number, because the mean of its divisors is an integer number (7171318620).

Almost surely, 2^21513955857 is an apocalyptic number.

It is an amenable number.

21513955857 is a deficient number, since it is larger than the sum of its proper divisors (7171318623).

21513955857 is an equidigital number, since it uses as much as digits as its factorization.

21513955857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7171318622.

The product of its digits is 1890000, while the sum is 51.

The spelling of 21513955857 in words is "twenty-one billion, five hundred thirteen million, nine hundred fifty-five thousand, eight hundred fifty-seven".