21399387 has 4 divisors (see below), whose sum is σ = 28532520. Its totient is φ = 14266256.

The previous prime is 21399353. The next prime is 21399401. The reversal of 21399387 is 78399312.

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 21399387 - 2¹² = 21395291 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21399307) 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 3 ways as a sum of consecutive naturals, for example, 3566562 + ... + 3566567.

It is an arithmetic number, because the mean of its divisors is an integer number (7133130).

Almost surely, 2^21399387 is an apocalyptic number.

21399387 is a deficient number, since it is larger than the sum of its proper divisors (7133133).

21399387 is an equidigital number, since it uses as much as digits as its factorization.

21399387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7133132.

The product of its digits is 81648, while the sum is 42.

The square root of 21399387 is about 4625.9471462610. The cubic root of 21399387 is about 277.6304589087.

The spelling of 21399387 in words is "twenty-one million, three hundred ninety-nine thousand, three hundred eighty-seven".