21805390 has 32 divisors (see below), whose sum is σ = 43001280. Its totient is φ = 7924224.

The previous prime is 21805367. The next prime is 21805391. The reversal of 21805390 is 9350812.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21805391) 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 15 ways as a sum of consecutive naturals, for example, 2719 + ... + 7141.

It is an arithmetic number, because the mean of its divisors is an integer number (1343790).

Almost surely, 2^21805390 is an apocalyptic number.

21805390 is a deficient number, since it is larger than the sum of its proper divisors (21195890).

21805390 is a wasteful number, since it uses less digits than its factorization.

21805390 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4476.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21805390 is about 4669.6241818802. The cubic root of 21805390 is about 279.3752652948.

The spelling of 21805390 in words is "twenty-one million, eight hundred five thousand, three hundred ninety".