21723915 has 16 divisors (see below), whose sum is σ = 34848000. Its totient is φ = 11556192.

The previous prime is 21723913. The next prime is 21723931. The reversal of 21723915 is 51932712.

It is not a de Polignac number, because 21723915 - 2¹ = 21723913 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21723913) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4936 + ... + 8234.

It is an arithmetic number, because the mean of its divisors is an integer number (2178000).

Almost surely, 2^21723915 is an apocalyptic number.

21723915 is a deficient number, since it is larger than the sum of its proper divisors (13124085).

21723915 is a wasteful number, since it uses less digits than its factorization.

21723915 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3746.

The product of its digits is 3780, while the sum is 30.

The square root of 21723915 is about 4660.8920819946. The cubic root of 21723915 is about 279.0268727087.

The spelling of 21723915 in words is "twenty-one million, seven hundred twenty-three thousand, nine hundred fifteen".