21689813 has 4 divisors (see below), whose sum is σ = 21715980. Its totient is φ = 21663648.

The previous prime is 21689803. The next prime is 21689821. The reversal of 21689813 is 31898612.

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 17123044 + 4566769 = 4138^2 + 2137^2 .

It is a cyclic number.

It is not a de Polignac number, because 21689813 - 2⁴ = 21689797 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21689803) 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, 11798 + ... + 13511.

It is an arithmetic number, because the mean of its divisors is an integer number (5428995).

Almost surely, 2^21689813 is an apocalyptic number.

It is an amenable number.

21689813 is a deficient number, since it is larger than the sum of its proper divisors (26167).

21689813 is an equidigital number, since it uses as much as digits as its factorization.

21689813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26166.

The product of its digits is 20736, while the sum is 38.

The square root of 21689813 is about 4657.2323326199. The cubic root of 21689813 is about 278.8807916453.

The spelling of 21689813 in words is "twenty-one million, six hundred eighty-nine thousand, eight hundred thirteen".