21000904 has 16 divisors (see below), whose sum is σ = 40441500. Its totient is φ = 10216512.

The previous prime is 21000893. The next prime is 21000907. The reversal of 21000904 is 40900012.

It can be written as a sum of positive squares in 2 ways, for example, as 18472804 + 2528100 = 4298^2 + 1590^2 .

It is not an unprimeable number, because it can be changed into a prime (21000907) 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, 35179 + ... + 35770.

Almost surely, 2^21000904 is an apocalyptic number.

It is an amenable number.

21000904 is a deficient number, since it is larger than the sum of its proper divisors (19440596).

21000904 is a wasteful number, since it uses less digits than its factorization.

21000904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 70992 (or 70988 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 21000904 is about 4582.6743283808. The cubic root of 21000904 is about 275.8963764185.

Adding to 21000904 its reverse (40900012), we get a palindrome (61900916).

It can be divided in two parts, 21000 and 904, that added together give a square (21904 = 148²).

The spelling of 21000904 in words is "twenty-one million, nine hundred four", and thus it is an aban number.