21387215 has 4 divisors (see below), whose sum is σ = 25664664. Its totient is φ = 17109768.

The previous prime is 21387203. The next prime is 21387227. The reversal of 21387215 is 51278312.

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

It is an interprime number because it is at equal distance from previous prime (21387203) and next prime (21387227).

It is a cyclic number.

It is not a de Polignac number, because 21387215 - 2⁶ = 21387151 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2138717 + ... + 2138726.

It is an arithmetic number, because the mean of its divisors is an integer number (6416166).

Almost surely, 2^21387215 is an apocalyptic number.

21387215 is a deficient number, since it is larger than the sum of its proper divisors (4277449).

21387215 is an equidigital number, since it uses as much as digits as its factorization.

21387215 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4277448.

The product of its digits is 3360, while the sum is 29.

The square root of 21387215 is about 4624.6313366581. The cubic root of 21387215 is about 277.5778100662.

The spelling of 21387215 in words is "twenty-one million, three hundred eighty-seven thousand, two hundred fifteen".