21357989 has 4 divisors (see below), whose sum is σ = 21370656. Its totient is φ = 21345324.

The previous prime is 21357983. The next prime is 21357997. The reversal of 21357989 is 98975312.

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 21357989 - 2²⁴ = 4580773 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 (21357983) 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, 3329 + ... + 7334.

It is an arithmetic number, because the mean of its divisors is an integer number (5342664).

Almost surely, 2^21357989 is an apocalyptic number.

It is an amenable number.

21357989 is a deficient number, since it is larger than the sum of its proper divisors (12667).

21357989 is a wasteful number, since it uses less digits than its factorization.

21357989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12666.

The product of its digits is 136080, while the sum is 44.

The square root of 21357989 is about 4621.4704369930. The cubic root of 21357989 is about 277.4513141329.

The spelling of 21357989 in words is "twenty-one million, three hundred fifty-seven thousand, nine hundred eighty-nine".