21000723 has 4 divisors (see below), whose sum is σ = 28000968. Its totient is φ = 14000480.

The previous prime is 21000709. The next prime is 21000731. The reversal of 21000723 is 32700012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21000723 - 2⁸ = 21000467 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21000823) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3500118 + ... + 3500123.

It is an arithmetic number, because the mean of its divisors is an integer number (7000242).

Almost surely, 2^21000723 is an apocalyptic number.

21000723 is a deficient number, since it is larger than the sum of its proper divisors (7000245).

21000723 is an equidigital number, since it uses as much as digits as its factorization.

21000723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7000244.

The product of its (nonzero) digits is 84, while the sum is 15.

The square root of 21000723 is about 4582.6545800442. The cubic root of 21000723 is about 275.8955837957.

Adding to 21000723 its reverse (32700012), we get a palindrome (53700735).

The spelling of 21000723 in words is "twenty-one million, seven hundred twenty-three", and thus it is an aban number.