21188765 has 16 divisors (see below), whose sum is σ = 27548976. Its totient is φ = 15552000.

The previous prime is 21188747. The next prime is 21188789. The reversal of 21188765 is 56788112.

It can be written as a sum of positive squares in 8 ways, for example, as 11215801 + 9972964 = 3349^2 + 3158^2 .

It is not a de Polignac number, because 21188765 - 2⁶ = 21188701 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10865 + ... + 12665.

It is an arithmetic number, because the mean of its divisors is an integer number (1721811).

Almost surely, 2^21188765 is an apocalyptic number.

It is an amenable number.

21188765 is a deficient number, since it is larger than the sum of its proper divisors (6360211).

21188765 is a wasteful number, since it uses less digits than its factorization.

21188765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2000.

The product of its digits is 26880, while the sum is 38.

The square root of 21188765 is about 4603.1255685675. The cubic root of 21188765 is about 276.7166012029.

The spelling of 21188765 in words is "twenty-one million, one hundred eighty-eight thousand, seven hundred sixty-five".