21805408 has 12 divisors (see below), whose sum is σ = 42929460. Its totient is φ = 10902688.

The previous prime is 21805391. The next prime is 21805411. The reversal of 21805408 is 80450812.

It is a congruent number.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 340678 + ... + 340741.

It is an arithmetic number, because the mean of its divisors is an integer number (3577455).

Almost surely, 2^21805408 is an apocalyptic number.

It is an amenable number.

21805408 is a deficient number, since it is larger than the sum of its proper divisors (21124052).

21805408 is an equidigital number, since it uses as much as digits as its factorization.

21805408 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 681429 (or 681421 counting only the distinct ones).

The product of its (nonzero) digits is 2560, while the sum is 28.

The square root of 21805408 is about 4669.6261092297. The cubic root of 21805408 is about 279.3753421680.

The spelling of 21805408 in words is "twenty-one million, eight hundred five thousand, four hundred eight".