21387213 has 8 divisors (see below), whose sum is σ = 31684800. Its totient is φ = 14258124.

The previous prime is 21387203. The next prime is 21387227. The reversal of 21387213 is 31278312.

It is not a de Polignac number, because 21387213 - 2¹³ = 21379021 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 792119 = 21387213 / (2 + 1 + 3 + 8 + 7 + 2 + 1 + 3).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21387203) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 396033 + ... + 396086.

It is an arithmetic number, because the mean of its divisors is an integer number (3960600).

Almost surely, 2^21387213 is an apocalyptic number.

It is an amenable number.

21387213 is a deficient number, since it is larger than the sum of its proper divisors (10297587).

21387213 is an equidigital number, since it uses as much as digits as its factorization.

21387213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 792128 (or 792122 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21387213 is about 4624.6311204246. The cubic root of 21387213 is about 277.5778014138.

The spelling of 21387213 in words is "twenty-one million, three hundred eighty-seven thousand, two hundred thirteen".