21423501557 has 4 divisors (see below), whose sum is σ = 22162243020. Its totient is φ = 20684760096.

The previous prime is 21423501551. The next prime is 21423501559. The reversal of 21423501557 is 75510532412.

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 6840282436 + 14583219121 = 82706^2 + 120761^2 .

It is a cyclic number.

It is not a de Polignac number, because 21423501557 - 2⁸ = 21423501301 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 (21423501551) 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, 369370688 + ... + 369370745.

It is an arithmetic number, because the mean of its divisors is an integer number (5540560755).

Almost surely, 2^21423501557 is an apocalyptic number.

It is an amenable number.

21423501557 is a deficient number, since it is larger than the sum of its proper divisors (738741463).

21423501557 is an equidigital number, since it uses as much as digits as its factorization.

21423501557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 738741462.

The product of its (nonzero) digits is 42000, while the sum is 35.

The spelling of 21423501557 in words is "twenty-one billion, four hundred twenty-three million, five hundred one thousand, five hundred fifty-seven".