21309387 has 8 divisors (see below), whose sum is σ = 30995520. Its totient is φ = 12914760.

The previous prime is 21309383. The next prime is 21309397. The reversal of 21309387 is 78390312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21309387 - 2² = 21309383 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33), and also a Moran number because the ratio is a prime number: 645739 = 21309387 / (2 + 1 + 3 + 0 + 9 + 3 + 8 + 7).

It is not an unprimeable number, because it can be changed into a prime (21309383) 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 7 ways as a sum of consecutive naturals, for example, 322837 + ... + 322902.

It is an arithmetic number, because the mean of its divisors is an integer number (3874440).

Almost surely, 2^21309387 is an apocalyptic number.

21309387 is a deficient number, since it is larger than the sum of its proper divisors (9686133).

21309387 is a wasteful number, since it uses less digits than its factorization.

21309387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 645753.

The product of its (nonzero) digits is 9072, while the sum is 33.

The square root of 21309387 is about 4616.2091590395. The cubic root of 21309387 is about 277.2406992625.

Adding to 21309387 its reverse (78390312), we get a palindrome (99699699).

The spelling of 21309387 in words is "twenty-one million, three hundred nine thousand, three hundred eighty-seven".