20665521 has 12 divisors (see below), whose sum is σ = 31421520. Its totient is φ = 13051800.

The previous prime is 20665501. The next prime is 20665529. The reversal of 20665521 is 12556602.

20665521 is a `hidden beast` number, since 2 + 0 + 6 + 655 + 2 + 1 = 666.

It is not a de Polignac number, because 20665521 - 2⁹ = 20665009 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20665529) 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 11 ways as a sum of consecutive naturals, for example, 60255 + ... + 60596.

It is an arithmetic number, because the mean of its divisors is an integer number (2618460).

Almost surely, 2^20665521 is an apocalyptic number.

It is an amenable number.

20665521 is a deficient number, since it is larger than the sum of its proper divisors (10755999).

20665521 is a wasteful number, since it uses less digits than its factorization.

20665521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 120876 (or 120873 counting only the distinct ones).

The product of its (nonzero) digits is 3600, while the sum is 27.

The square root of 20665521 is about 4545.9345573820. The cubic root of 20665521 is about 274.4198059706.

The spelling of 20665521 in words is "twenty million, six hundred sixty-five thousand, five hundred twenty-one".