21091904 has 28 divisors (see below), whose sum is σ = 43208448. Its totient is φ = 10204800.

The previous prime is 21091901. The next prime is 21091913. The reversal of 21091904 is 40919012.

It is not an unprimeable number, because it can be changed into a prime (21091901) 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, 3332 + ... + 7299.

Almost surely, 2^21091904 is an apocalyptic number.

It is an amenable number.

21091904 is an abundant number, since it is smaller than the sum of its proper divisors (22116544).

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

21091904 is a wasteful number, since it uses less digits than its factorization.

21091904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10674 (or 10664 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 26.

The square root of 21091904 is about 4592.5922962963. The cubic root of 21091904 is about 276.2943020478.

The spelling of 21091904 in words is "twenty-one million, ninety-one thousand, nine hundred four".