21705866 has 32 divisors (see below), whose sum is σ = 42188160. Its totient is φ = 8133696.

The previous prime is 21705863. The next prime is 21705883. The reversal of 21705866 is 66850712.

It is a super-2 number, since 2×21705866² = 942289237619912, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21705863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 320 + ... + 6596.

It is an arithmetic number, because the mean of its divisors is an integer number (1318380).

Almost surely, 2^21705866 is an apocalyptic number.

21705866 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

21705866 is a deficient number, since it is larger than the sum of its proper divisors (20482294).

21705866 is a wasteful number, since it uses less digits than its factorization.

21705866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6318.

The product of its (nonzero) digits is 20160, while the sum is 35.

The square root of 21705866 is about 4658.9554623327. The cubic root of 21705866 is about 278.9495761531.

The spelling of 21705866 in words is "twenty-one million, seven hundred five thousand, eight hundred sixty-six".