21705047 has 16 divisors (see below), whose sum is σ = 26924352. Its totient is φ = 17038080.

The previous prime is 21705041. The next prime is 21705071. The reversal of 21705047 is 74050712.

It is a cyclic number.

It is not a de Polignac number, because 21705047 - 2⁸ = 21704791 is a prime.

It is a super-3 number, since 3×21705047³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21705041) 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, 11597 + ... + 13337.

It is an arithmetic number, because the mean of its divisors is an integer number (1682772).

Almost surely, 2^21705047 is an apocalyptic number.

21705047 is a deficient number, since it is larger than the sum of its proper divisors (5219305).

21705047 is a wasteful number, since it uses less digits than its factorization.

21705047 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1898.

The product of its (nonzero) digits is 1960, while the sum is 26.

The square root of 21705047 is about 4658.8675662654. The cubic root of 21705047 is about 278.9460676917.

Adding to 21705047 its reverse (74050712), we get a palindrome (95755759).

The spelling of 21705047 in words is "twenty-one million, seven hundred five thousand, forty-seven".