21043639 has 8 divisors (see below), whose sum is σ = 22074048. Its totient is φ = 20037600.

The previous prime is 21043613. The next prime is 21043661. The reversal of 21043639 is 93634012.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21043639 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 (21043609) 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, 4312 + ... + 7789.

It is an arithmetic number, because the mean of its divisors is an integer number (2759256).

Almost surely, 2^21043639 is an apocalyptic number.

21043639 is a deficient number, since it is larger than the sum of its proper divisors (1030409).

21043639 is a wasteful number, since it uses less digits than its factorization.

21043639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12185.

The product of its (nonzero) digits is 3888, while the sum is 28.

The square root of 21043639 is about 4587.3346291719. The cubic root of 21043639 is about 276.0833912756.

The spelling of 21043639 in words is "twenty-one million, forty-three thousand, six hundred thirty-nine".