21666685 has 4 divisors (see below), whose sum is σ = 26000028. Its totient is φ = 17333344.

The previous prime is 21666679. The next prime is 21666691. The reversal of 21666685 is 58666612.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21666679) and next prime (21666691).

It can be written as a sum of positive squares in 2 ways, for example, as 14032516 + 7634169 = 3746^2 + 2763^2 .

It is a cyclic number.

It is not a de Polignac number, because 21666685 - 2³ = 21666677 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2166664 + ... + 2166673.

It is an arithmetic number, because the mean of its divisors is an integer number (6500007).

Almost surely, 2^21666685 is an apocalyptic number.

It is an amenable number.

21666685 is a deficient number, since it is larger than the sum of its proper divisors (4333343).

21666685 is an equidigital number, since it uses as much as digits as its factorization.

21666685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4333342.

The product of its digits is 103680, while the sum is 40.

The square root of 21666685 is about 4654.7486505718. The cubic root of 21666685 is about 278.7816322096.

The spelling of 21666685 in words is "twenty-one million, six hundred sixty-six thousand, six hundred eighty-five".