21153765 has 16 divisors (see below), whose sum is σ = 34026048. Its totient is φ = 11222016.

The previous prime is 21153761. The next prime is 21153791. The reversal of 21153765 is 56735112.

It is not a de Polignac number, because 21153765 - 2² = 21153761 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21153761) 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 15 ways as a sum of consecutive naturals, for example, 759 + ... + 6548.

It is an arithmetic number, because the mean of its divisors is an integer number (2126628).

Almost surely, 2^21153765 is an apocalyptic number.

It is an amenable number.

21153765 is a deficient number, since it is larger than the sum of its proper divisors (12872283).

21153765 is a wasteful number, since it uses less digits than its factorization.

21153765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7508.

The product of its digits is 6300, while the sum is 30.

The square root of 21153765 is about 4599.3222326773. The cubic root of 21153765 is about 276.5641553414.

Adding to 21153765 its reverse (56735112), we get a palindrome (77888877).

The spelling of 21153765 in words is "twenty-one million, one hundred fifty-three thousand, seven hundred sixty-five".