20905865 has 4 divisors (see below), whose sum is σ = 25087044. Its totient is φ = 16724688.

The previous prime is 20905861. The next prime is 20905877. The reversal of 20905865 is 56850902.

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 3625216 + 17280649 = 1904^2 + 4157^2 .

It is a cyclic number.

It is not a de Polignac number, because 20905865 - 2² = 20905861 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20905861) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2090582 + ... + 2090591.

It is an arithmetic number, because the mean of its divisors is an integer number (6271761).

Almost surely, 2^20905865 is an apocalyptic number.

It is an amenable number.

20905865 is a deficient number, since it is larger than the sum of its proper divisors (4181179).

20905865 is an equidigital number, since it uses as much as digits as its factorization.

20905865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4181178.

The product of its (nonzero) digits is 21600, while the sum is 35.

The square root of 20905865 is about 4572.2931883247. The cubic root of 20905865 is about 275.4795599255.

The spelling of 20905865 in words is "twenty million, nine hundred five thousand, eight hundred sixty-five".