21604493 has 4 divisors (see below), whose sum is σ = 21617820. Its totient is φ = 21591168.

The previous prime is 21604487. The next prime is 21604523. The reversal of 21604493 is 39440612.

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 8369449 + 13235044 = 2893^2 + 3638^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21604493 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 (21604393) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3830 + ... + 7607.

It is an arithmetic number, because the mean of its divisors is an integer number (5404455).

Almost surely, 2^21604493 is an apocalyptic number.

It is an amenable number.

21604493 is a deficient number, since it is larger than the sum of its proper divisors (13327).

21604493 is a wasteful number, since it uses less digits than its factorization.

21604493 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13326.

The product of its (nonzero) digits is 5184, while the sum is 29.

The square root of 21604493 is about 4648.0633601533. The cubic root of 21604493 is about 278.5146385471.

The spelling of 21604493 in words is "twenty-one million, six hundred four thousand, four hundred ninety-three".