21157559 has 4 divisors (see below), whose sum is σ = 21887160. Its totient is φ = 20427960.

The previous prime is 21157529. The next prime is 21157573. The reversal of 21157559 is 95575112.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21157559 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 (21157529) 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, 364757 + ... + 364814.

It is an arithmetic number, because the mean of its divisors is an integer number (5471790).

Almost surely, 2^21157559 is an apocalyptic number.

21157559 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

21157559 is a deficient number, since it is larger than the sum of its proper divisors (729601).

21157559 is an equidigital number, since it uses as much as digits as its factorization.

21157559 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 729600.

The product of its digits is 15750, while the sum is 35.

The square root of 21157559 is about 4599.7346662607. The cubic root of 21157559 is about 276.5806885949.

The spelling of 21157559 in words is "twenty-one million, one hundred fifty-seven thousand, five hundred fifty-nine".