21608557 has 4 divisors (see below), whose sum is σ = 21655296. Its totient is φ = 21561820.

The previous prime is 21608551. The next prime is 21608603. The reversal of 21608557 is 75580612.

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 a cyclic number.

It is not a de Polignac number, because 21608557 - 2³ = 21608549 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 (21608551) 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, 22669 + ... + 23602.

It is an arithmetic number, because the mean of its divisors is an integer number (5413824).

Almost surely, 2^21608557 is an apocalyptic number.

It is an amenable number.

21608557 is a deficient number, since it is larger than the sum of its proper divisors (46739).

21608557 is an equidigital number, since it uses as much as digits as its factorization.

21608557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 46738.

The product of its (nonzero) digits is 16800, while the sum is 34.

The square root of 21608557 is about 4648.5005109175. The cubic root of 21608557 is about 278.5321011574.

The spelling of 21608557 in words is "twenty-one million, six hundred eight thousand, five hundred fifty-seven".