20640709 has 4 divisors (see below), whose sum is σ = 21198604. Its totient is φ = 20082816.

The previous prime is 20640679. The next prime is 20640713. The reversal of 20640709 is 90704602.

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 15249025 + 5391684 = 3905^2 + 2322^2 .

It is a cyclic number.

It is not a de Polignac number, because 20640709 - 2¹¹ = 20638661 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20649709) 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, 278892 + ... + 278965.

It is an arithmetic number, because the mean of its divisors is an integer number (5299651).

Almost surely, 2^20640709 is an apocalyptic number.

It is an amenable number.

20640709 is a deficient number, since it is larger than the sum of its proper divisors (557895).

20640709 is an equidigital number, since it uses as much as digits as its factorization.

20640709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 557894.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 20640709 is about 4543.2047059317. The cubic root of 20640709 is about 274.3099348625.

The spelling of 20640709 in words is "twenty million, six hundred forty thousand, seven hundred nine".