21705838 has 32 divisors (see below), whose sum is σ = 42985728. Its totient is φ = 7958400.

The previous prime is 21705829. The next prime is 21705839. The reversal of 21705838 is 83850712.

It is a super-2 number, since 2×21705838² = 942286806564488, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (34).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21705839) by changing a digit.

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, 1528 + ... + 6763.

It is an arithmetic number, because the mean of its divisors is an integer number (1343304).

Almost surely, 2^21705838 is an apocalyptic number.

21705838 is a deficient number, since it is larger than the sum of its proper divisors (21279890).

21705838 is a wasteful number, since it uses less digits than its factorization.

21705838 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8328.

The product of its (nonzero) digits is 13440, while the sum is 34.

The square root of 21705838 is about 4658.9524573664. The cubic root of 21705838 is about 278.9494562072.

It can be divided in two parts, 2170 and 5838, that added together give a palindrome (8008).

The spelling of 21705838 in words is "twenty-one million, seven hundred five thousand, eight hundred thirty-eight".