21705398 has 32 divisors (see below), whose sum is σ = 39584160. Its totient is φ = 8789760.

The previous prime is 21705389. The next prime is 21705401. The reversal of 21705398 is 89350712.

It is a super-2 number, since 2×21705398² = 942248604676808, which contains 22 as substring.

It is a Smith number, since the sum of its digits (35) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6986 + ... + 9602.

It is an arithmetic number, because the mean of its divisors is an integer number (1237005).

Almost surely, 2^21705398 is an apocalyptic number.

21705398 is a deficient number, since it is larger than the sum of its proper divisors (17878762).

21705398 is a wasteful number, since it uses less digits than its factorization.

21705398 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2672.

The product of its (nonzero) digits is 15120, while the sum is 35.

The square root of 21705398 is about 4658.9052362116. The cubic root of 21705398 is about 278.9475713289.

The spelling of 21705398 in words is "twenty-one million, seven hundred five thousand, three hundred ninety-eight".