20665309 has 6 divisors (see below), whose sum is σ = 24039294. Its totient is φ = 17713080.

The previous prime is 20665297. The next prime is 20665357. The reversal of 20665309 is 90356602.

It can be written as a sum of positive squares in only one way, i.e., 18896409 + 1768900 = 4347^2 + 1330^2 .

It is not a de Polignac number, because 20665309 - 2¹⁷ = 20534237 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 (20665009) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 210822 + ... + 210919.

It is an arithmetic number, because the mean of its divisors is an integer number (4006549).

Almost surely, 2^20665309 is an apocalyptic number.

It is an amenable number.

20665309 is a deficient number, since it is larger than the sum of its proper divisors (3373985).

20665309 is an equidigital number, since it uses as much as digits as its factorization.

20665309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 421755 (or 421748 counting only the distinct ones).

The product of its (nonzero) digits is 9720, while the sum is 31.

The square root of 20665309 is about 4545.9112397846. The cubic root of 20665309 is about 274.4188675767.

The spelling of 20665309 in words is "twenty million, six hundred sixty-five thousand, three hundred nine".