21408739 has 8 divisors (see below), whose sum is σ = 23458032. Its totient is φ = 19376640.

The previous prime is 21408733. The next prime is 21408781. The reversal of 21408739 is 93780412.

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

It is a cyclic number.

It is not a de Polignac number, because 21408739 - 2⁹ = 21408227 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21408733) 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, 1614 + ... + 6739.

It is an arithmetic number, because the mean of its divisors is an integer number (2932254).

Almost surely, 2^21408739 is an apocalyptic number.

21408739 is a deficient number, since it is larger than the sum of its proper divisors (2049293).

21408739 is a wasteful number, since it uses less digits than its factorization.

21408739 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8597.

The product of its (nonzero) digits is 12096, while the sum is 34.

The square root of 21408739 is about 4626.9578558703. The cubic root of 21408739 is about 277.6708965455.

The spelling of 21408739 in words is "twenty-one million, four hundred eight thousand, seven hundred thirty-nine".