21428718517 has 4 divisors (see below), whose sum is σ = 21520687500. Its totient is φ = 21336749536.

The previous prime is 21428718503. The next prime is 21428718551. The reversal of 21428718517 is 71581782412.

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 4759068196 + 16669650321 = 68986^2 + 129111^2 .

It is a cyclic number.

It is not a de Polignac number, because 21428718517 - 2¹¹ = 21428716469 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 (21428718557) 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, 45984142 + ... + 45984607.

It is an arithmetic number, because the mean of its divisors is an integer number (5380171875).

Almost surely, 2^21428718517 is an apocalyptic number.

It is an amenable number.

21428718517 is a deficient number, since it is larger than the sum of its proper divisors (91968983).

21428718517 is an equidigital number, since it uses as much as digits as its factorization.

21428718517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91968982.

The product of its digits is 250880, while the sum is 46.

The spelling of 21428718517 in words is "twenty-one billion, four hundred twenty-eight million, seven hundred eighteen thousand, five hundred seventeen".