21020004 has 72 divisors (see below), whose sum is σ = 56784000. Its totient is φ = 6537024.

The previous prime is 21019993. The next prime is 21020011. The reversal of 21020004 is 40002012.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 53842 + ... + 54230.

Almost surely, 2^21020004 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21020004, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28392000).

21020004 is an abundant number, since it is smaller than the sum of its proper divisors (35763996).

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

21020004 is a wasteful number, since it uses less digits than its factorization.

21020004 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 497 (or 492 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 9.

The square root of 21020004 is about 4584.7577907671. The cubic root of 21020004 is about 275.9799922484.

Adding to 21020004 its reverse (40002012), we get a palindrome (61022016).

The spelling of 21020004 in words is "twenty-one million, twenty thousand, four".