21904509 has 12 divisors (see below), whose sum is σ = 32103008. Its totient is φ = 13275240.

The previous prime is 21904489. The next prime is 21904523. The reversal of 21904509 is 90540912.

It is a happy number.

It is a de Polignac number, because none of the positive numbers 2^k-21904509 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21904559) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 29809 + ... + 30534.

Almost surely, 2^21904509 is an apocalyptic number.

It is an amenable number.

21904509 is a deficient number, since it is larger than the sum of its proper divisors (10198499).

21904509 is a wasteful number, since it uses less digits than its factorization.

21904509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 60368 (or 60357 counting only the distinct ones).

The product of its (nonzero) digits is 3240, while the sum is 30.

The square root of 21904509 is about 4680.2253150890. The cubic root of 21904509 is about 279.7979366981.

The spelling of 21904509 in words is "twenty-one million, nine hundred four thousand, five hundred nine".