21039744 has 128 divisors (see below), whose sum is σ = 64774080. Its totient is φ = 5980160.

The previous prime is 21039721. The next prime is 21039749. The reversal of 21039744 is 44793012.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (128).

It is not an unprimeable number, because it can be changed into a prime (21039749) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 71662 + ... + 71954.

Almost surely, 2^21039744 is an apocalyptic number.

21039744 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21039744, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32387040).

21039744 is an abundant number, since it is smaller than the sum of its proper divisors (43734336).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21039744 is a wasteful number, since it uses less digits than its factorization.

21039744 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 338 (or 326 counting only the distinct ones).

The product of its (nonzero) digits is 6048, while the sum is 30.

The square root of 21039744 is about 4586.9100710609. The cubic root of 21039744 is about 276.0663566559.

The spelling of 21039744 in words is "twenty-one million, thirty-nine thousand, seven hundred forty-four".