21003638 has 4 divisors (see below), whose sum is σ = 31505460. Its totient is φ = 10501818.

The previous prime is 21003637. The next prime is 21003659. The reversal of 21003638 is 83630012.

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

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 pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5250908 + ... + 5250911.

It is an arithmetic number, because the mean of its divisors is an integer number (7876365).

Almost surely, 2^21003638 is an apocalyptic number.

21003638 is a deficient number, since it is larger than the sum of its proper divisors (10501822).

21003638 is a wasteful number, since it uses less digits than its factorization.

21003638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10501821.

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 21003638 is about 4582.9726161085. The cubic root of 21003638 is about 275.9083484105.

The spelling of 21003638 in words is "twenty-one million, three thousand, six hundred thirty-eight".