21507685 has 16 divisors (see below), whose sum is σ = 26462592. Its totient is φ = 16776000.

The previous prime is 21507667. The next prime is 21507701. The reversal of 21507685 is 58670512.

It is not a de Polignac number, because 21507685 - 2⁵ = 21507653 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21507685.

It is a congruent number.

It is an unprimeable number.

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, 45822 + ... + 46288.

It is an arithmetic number, because the mean of its divisors is an integer number (1653912).

Almost surely, 2^21507685 is an apocalyptic number.

It is an amenable number.

21507685 is a deficient number, since it is larger than the sum of its proper divisors (4954907).

21507685 is a wasteful number, since it uses less digits than its factorization.

21507685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 684.

The product of its (nonzero) digits is 16800, while the sum is 34.

The square root of 21507685 is about 4637.6378685706. The cubic root of 21507685 is about 278.0980150564.

The spelling of 21507685 in words is "twenty-one million, five hundred seven thousand, six hundred eighty-five".