21557087 has 4 divisors (see below), whose sum is σ = 21714576. Its totient is φ = 21399600.

The previous prime is 21557057. The next prime is 21557099. The reversal of 21557087 is 78075512.

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

It is a cyclic number.

It is not a de Polignac number, because 21557087 - 2⁶ = 21557023 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 (21557017) 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, 78539 + ... + 78812.

It is an arithmetic number, because the mean of its divisors is an integer number (5428644).

Almost surely, 2^21557087 is an apocalyptic number.

21557087 is a deficient number, since it is larger than the sum of its proper divisors (157489).

21557087 is a wasteful number, since it uses less digits than its factorization.

21557087 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 157488.

The product of its (nonzero) digits is 19600, while the sum is 35.

The square root of 21557087 is about 4642.9610164204. The cubic root of 21557087 is about 278.3107776511.

The spelling of 21557087 in words is "twenty-one million, five hundred fifty-seven thousand, eighty-seven".