20856565 has 4 divisors (see below), whose sum is σ = 25027884. Its totient is φ = 16685248.

The previous prime is 20856551. The next prime is 20856599. The reversal of 20856565 is 56565802.

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 6041764 + 14814801 = 2458^2 + 3849^2 .

It is a cyclic number.

It is not a de Polignac number, because 20856565 - 2¹⁷ = 20725493 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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, 2085652 + ... + 2085661.

It is an arithmetic number, because the mean of its divisors is an integer number (6256971).

Almost surely, 2^20856565 is an apocalyptic number.

It is an amenable number.

20856565 is a deficient number, since it is larger than the sum of its proper divisors (4171319).

20856565 is an equidigital number, since it uses as much as digits as its factorization.

20856565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4171318.

The product of its (nonzero) digits is 72000, while the sum is 37.

The square root of 20856565 is about 4566.8988383804. The cubic root of 20856565 is about 275.2628451112.

The spelling of 20856565 in words is "twenty million, eight hundred fifty-six thousand, five hundred sixty-five".