21705537 has 16 divisors (see below), whose sum is σ = 34513920. Its totient is φ = 11863632.

The previous prime is 21705529. The next prime is 21705539. The reversal of 21705537 is 73550712.

It is not a de Polignac number, because 21705537 - 2³ = 21705529 is a prime.

It is a super-2 number, since 2×21705537² = 942260672916738, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21705539) 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, 21987 + ... + 22952.

It is an arithmetic number, because the mean of its divisors is an integer number (2157120).

Almost surely, 2^21705537 is an apocalyptic number.

It is an amenable number.

21705537 is a deficient number, since it is larger than the sum of its proper divisors (12808383).

21705537 is a wasteful number, since it uses less digits than its factorization.

21705537 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44972.

The product of its (nonzero) digits is 7350, while the sum is 30.

The square root of 21705537 is about 4658.9201538554. The cubic root of 21705537 is about 278.9481667818.

The spelling of 21705537 in words is "twenty-one million, seven hundred five thousand, five hundred thirty-seven".