21004405 has 16 divisors (see below), whose sum is σ = 27688320. Its totient is φ = 15225408.

The previous prime is 21004387. The next prime is 21004447. The reversal of 21004405 is 50440012.

It is a cyclic number.

It is not a de Polignac number, because 21004405 - 2⁹ = 21003893 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2622 + ... + 6991.

It is an arithmetic number, because the mean of its divisors is an integer number (1730520).

Almost surely, 2^21004405 is an apocalyptic number.

It is an amenable number.

21004405 is a deficient number, since it is larger than the sum of its proper divisors (6683915).

21004405 is a wasteful number, since it uses less digits than its factorization.

21004405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9660.

The product of its (nonzero) digits is 160, while the sum is 16.

The square root of 21004405 is about 4583.0562946575. The cubic root of 21004405 is about 275.9117068625.

Adding to 21004405 its reverse (50440012), we get a palindrome (71444417).

The spelling of 21004405 in words is "twenty-one million, four thousand, four hundred five".