21905215 has 4 divisors (see below), whose sum is σ = 26286264. Its totient is φ = 17524168.

The previous prime is 21905209. The next prime is 21905227. The reversal of 21905215 is 51250912.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21905215 - 2¹⁵ = 21872447 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21905215.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2190517 + ... + 2190526.

It is an arithmetic number, because the mean of its divisors is an integer number (6571566).

Almost surely, 2^21905215 is an apocalyptic number.

21905215 is a deficient number, since it is larger than the sum of its proper divisors (4381049).

21905215 is an equidigital number, since it uses as much as digits as its factorization.

21905215 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4381048.

The product of its (nonzero) digits is 900, while the sum is 25.

The square root of 21905215 is about 4680.3007382005. The cubic root of 21905215 is about 279.8009427036.

The spelling of 21905215 in words is "twenty-one million, nine hundred five thousand, two hundred fifteen".