21105765 has 48 divisors (see below), whose sum is σ = 39312000. Its totient is φ = 10850112.

The previous prime is 21105757. The next prime is 21105767. The reversal of 21105765 is 56750112.

It is not a de Polignac number, because 21105765 - 2³ = 21105757 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105767) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 34936 + ... + 35534.

It is an arithmetic number, because the mean of its divisors is an integer number (819000).

Almost surely, 2^21105765 is an apocalyptic number.

It is an amenable number.

21105765 is a deficient number, since it is larger than the sum of its proper divisors (18206235).

21105765 is an equidigital number, since it uses as much as digits as its factorization.

21105765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 648 (or 636 counting only the distinct ones).

The product of its (nonzero) digits is 2100, while the sum is 27.

The square root of 21105765 is about 4594.1011090310. The cubic root of 21105765 is about 276.3548130492.

Adding to 21105765 its reverse (56750112), we get a palindrome (77855877).

It can be divided in two parts, 2110 and 5765, that added together give a triangular number (7875 = T₁₂₅).

The spelling of 21105765 in words is "twenty-one million, one hundred five thousand, seven hundred sixty-five".