21306647 has 4 divisors (see below), whose sum is σ = 21333360. Its totient is φ = 21279936.

The previous prime is 21306617. The next prime is 21306707. The reversal of 21306647 is 74660312.

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 21306647 - 2¹² = 21302551 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21306617) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12122 + ... + 13767.

It is an arithmetic number, because the mean of its divisors is an integer number (5333340).

Almost surely, 2^21306647 is an apocalyptic number.

21306647 is a deficient number, since it is larger than the sum of its proper divisors (26713).

21306647 is an equidigital number, since it uses as much as digits as its factorization.

21306647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26712.

The product of its (nonzero) digits is 6048, while the sum is 29.

The square root of 21306647 is about 4615.9123691855. The cubic root of 21306647 is about 277.2288160475.

Adding to 21306647 its reverse (74660312), we get a palindrome (95966959).

The spelling of 21306647 in words is "twenty-one million, three hundred six thousand, six hundred forty-seven".