21001904 has 40 divisors (see below), whose sum is σ = 50734848. Its totient is φ = 8182080.

The previous prime is 21001889. The next prime is 21001909. The reversal of 21001904 is 40910012.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21001909) 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, 7292 + ... + 9755.

Almost surely, 2^21001904 is an apocalyptic number.

It is an amenable number.

21001904 is an abundant number, since it is smaller than the sum of its proper divisors (29732944).

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

21001904 is a wasteful number, since it uses less digits than its factorization.

21001904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17073 (or 17067 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 17.

The square root of 21001904 is about 4582.7834336787. The cubic root of 21001904 is about 275.9007554681.

Adding to 21001904 its reverse (40910012), we get a palindrome (61911916).

It can be divided in two parts, 2100 and 1904, that added together give a palindrome (4004).

The spelling of 21001904 in words is "twenty-one million, one thousand, nine hundred four".