21605804 has 12 divisors (see below), whose sum is σ = 41247528. Its totient is φ = 9820800.

The previous prime is 21605803. The next prime is 21605807. The reversal of 21605804 is 40850612.

It is not an unprimeable number, because it can be changed into a prime (21605803) 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, 245477 + ... + 245564.

It is an arithmetic number, because the mean of its divisors is an integer number (3437294).

Almost surely, 2^21605804 is an apocalyptic number.

It is an amenable number.

21605804 is a deficient number, since it is larger than the sum of its proper divisors (19641724).

21605804 is a wasteful number, since it uses less digits than its factorization.

21605804 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 491056 (or 491054 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 26.

The square root of 21605804 is about 4648.2043844909. The cubic root of 21605804 is about 278.5202720251.

The spelling of 21605804 in words is "twenty-one million, six hundred five thousand, eight hundred four".