21023709 has 16 divisors (see below), whose sum is σ = 33722880. Its totient is φ = 11381040.

The previous prime is 21023701. The next prime is 21023731. The reversal of 21023709 is 90732012.

It is not a de Polignac number, because 21023709 - 2³ = 21023701 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21023701) 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, 25947 + ... + 26744.

It is an arithmetic number, because the mean of its divisors is an integer number (2107680).

Almost surely, 2^21023709 is an apocalyptic number.

It is an amenable number.

21023709 is a deficient number, since it is larger than the sum of its proper divisors (12699171).

21023709 is a wasteful number, since it uses less digits than its factorization.

21023709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52720.

The product of its (nonzero) digits is 756, while the sum is 24.

The square root of 21023709 is about 4585.1618292052. The cubic root of 21023709 is about 275.9962061020.

The spelling of 21023709 in words is "twenty-one million, twenty-three thousand, seven hundred nine".