21639307 has 4 divisors (see below), whose sum is σ = 22385520. Its totient is φ = 20893096.

The previous prime is 21639281. The next prime is 21639313. The reversal of 21639307 is 70393612.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21639307 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21639337) 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, 373063 + ... + 373120.

It is an arithmetic number, because the mean of its divisors is an integer number (5596380).

Almost surely, 2^21639307 is an apocalyptic number.

21639307 is a deficient number, since it is larger than the sum of its proper divisors (746213).

21639307 is an equidigital number, since it uses as much as digits as its factorization.

21639307 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 746212.

The product of its (nonzero) digits is 6804, while the sum is 31.

The square root of 21639307 is about 4651.8068532561. The cubic root of 21639307 is about 278.6641599924.

The spelling of 21639307 in words is "twenty-one million, six hundred thirty-nine thousand, three hundred seven".