20665509 has 16 divisors (see below), whose sum is σ = 28041024. Its totient is φ = 13536000.

The previous prime is 20665501. The next prime is 20665529. The reversal of 20665509 is 90556602.

It is not a de Polignac number, because 20665509 - 2³ = 20665501 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 20665509.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20665501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 72882 + ... + 73164.

It is an arithmetic number, because the mean of its divisors is an integer number (1752564).

Almost surely, 2^20665509 is an apocalyptic number.

It is an amenable number.

20665509 is a deficient number, since it is larger than the sum of its proper divisors (7375515).

20665509 is a wasteful number, since it uses less digits than its factorization.

20665509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 628.

The product of its (nonzero) digits is 16200, while the sum is 33.

The square root of 20665509 is about 4545.9332375212. The cubic root of 20665509 is about 274.4197528542.

Adding to 20665509 its reverse (90556602), we get a palindrome (111222111).

The spelling of 20665509 in words is "twenty million, six hundred sixty-five thousand, five hundred nine".