21705747 has 16 divisors (see below), whose sum is σ = 33530880. Its totient is φ = 12232512.

The previous prime is 21705743. The next prime is 21705773. The reversal of 21705747 is 74750712.

It is a happy number.

It is not a de Polignac number, because 21705747 - 2² = 21705743 is a prime.

It is a super-2 number, since 2×21705747² = 942278905656018, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21705743) 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, 5547 + ... + 8612.

It is an arithmetic number, because the mean of its divisors is an integer number (2095680).

Almost surely, 2^21705747 is an apocalyptic number.

21705747 is a deficient number, since it is larger than the sum of its proper divisors (11825133).

21705747 is a wasteful number, since it uses less digits than its factorization.

21705747 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14242.

The product of its (nonzero) digits is 13720, while the sum is 33.

The square root of 21705747 is about 4658.9426912122. The cubic root of 21705747 is about 278.9490663821.

The spelling of 21705747 in words is "twenty-one million, seven hundred five thousand, seven hundred forty-seven".