20665905 has 32 divisors (see below), whose sum is σ = 35925120. Its totient is φ = 10083840.

The previous prime is 20665867. The next prime is 20665907. The reversal of 20665905 is 50956602.

It is not a de Polignac number, because 20665905 - 2⁸ = 20665649 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20665907) 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 31 ways as a sum of consecutive naturals, for example, 25141 + ... + 25949.

It is an arithmetic number, because the mean of its divisors is an integer number (1122660).

Almost surely, 2^20665905 is an apocalyptic number.

It is an amenable number.

20665905 is a deficient number, since it is larger than the sum of its proper divisors (15259215).

20665905 is a wasteful number, since it uses less digits than its factorization.

20665905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 961.

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

The square root of 20665905 is about 4545.9767927256. The cubic root of 20665905 is about 274.4215056867.

The spelling of 20665905 in words is "twenty million, six hundred sixty-five thousand, nine hundred five".