21000685 has 4 divisors (see below), whose sum is σ = 25200828. Its totient is φ = 16800544.

The previous prime is 21000677. The next prime is 21000689. The reversal of 21000685 is 58600012.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 15515721 + 5484964 = 3939^2 + 2342^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000685 - 2³ = 21000677 is a prime.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000689) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2100064 + ... + 2100073.

It is an arithmetic number, because the mean of its divisors is an integer number (6300207).

Almost surely, 2^21000685 is an apocalyptic number.

It is an amenable number.

21000685 is a deficient number, since it is larger than the sum of its proper divisors (4200143).

21000685 is an equidigital number, since it uses as much as digits as its factorization.

21000685 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4200142.

The product of its (nonzero) digits is 480, while the sum is 22.

The square root of 21000685 is about 4582.6504339738. The cubic root of 21000685 is about 275.8954173881.

Adding to 21000685 its reverse (58600012), we get a palindrome (79600697).

The spelling of 21000685 in words is "twenty-one million, six hundred eighty-five", and thus it is an aban number.