21012765 has 32 divisors (see below), whose sum is σ = 37480320. Its totient is φ = 9990144.

The previous prime is 21012749. The next prime is 21012773. The reversal of 21012765 is 56721012.

It is not a de Polignac number, because 21012765 - 2⁴ = 21012749 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2677 + ... + 7013.

It is an arithmetic number, because the mean of its divisors is an integer number (1171260).

Almost surely, 2^21012765 is an apocalyptic number.

It is an amenable number.

21012765 is a deficient number, since it is larger than the sum of its proper divisors (16467555).

21012765 is a wasteful number, since it uses less digits than its factorization.

21012765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4381.

The product of its (nonzero) digits is 840, while the sum is 24.

The square root of 21012765 is about 4583.9682590524. The cubic root of 21012765 is about 275.9483073742.

Adding to 21012765 its reverse (56721012), we get a palindrome (77733777).

The spelling of 21012765 in words is "twenty-one million, twelve thousand, seven hundred sixty-five".