21003639 has 4 divisors (see below), whose sum is σ = 28004856. Its totient is φ = 14002424.

The previous prime is 21003637. The next prime is 21003659. The reversal of 21003639 is 93630012.

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 21003639 - 2¹ = 21003637 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21003637) 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, 3500604 + ... + 3500609.

It is an arithmetic number, because the mean of its divisors is an integer number (7001214).

Almost surely, 2^21003639 is an apocalyptic number.

21003639 is a deficient number, since it is larger than the sum of its proper divisors (7001217).

21003639 is an equidigital number, since it uses as much as digits as its factorization.

21003639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7001216.

The product of its (nonzero) digits is 972, while the sum is 24.

The square root of 21003639 is about 4582.9727252080. The cubic root of 21003639 is about 275.9083527893.

The spelling of 21003639 in words is "twenty-one million, three thousand, six hundred thirty-nine".