21008723 has 8 divisors (see below), whose sum is σ = 21481200. Its totient is φ = 20539168.

The previous prime is 21008681. The next prime is 21008749. The reversal of 21008723 is 32780012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21008723 - 2²⁰ = 19960147 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21008773) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 20108 + ... + 21126.

It is an arithmetic number, because the mean of its divisors is an integer number (2685150).

Almost surely, 2^21008723 is an apocalyptic number.

21008723 is a deficient number, since it is larger than the sum of its proper divisors (472477).

21008723 is a wasteful number, since it uses less digits than its factorization.

21008723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1461.

The product of its (nonzero) digits is 672, while the sum is 23.

The square root of 21008723 is about 4583.5273534692. The cubic root of 21008723 is about 275.9306125019.

Adding to 21008723 its reverse (32780012), we get a palindrome (53788735).

The spelling of 21008723 in words is "twenty-one million, eight thousand, seven hundred twenty-three".