21723818 has 4 divisors (see below), whose sum is σ = 32585730. Its totient is φ = 10861908.

The previous prime is 21723797. The next prime is 21723853. The reversal of 21723818 is 81832712.

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

It can be written as a sum of positive squares in only one way, i.e., 20729809 + 994009 = 4553^2 + 997^2 .

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5430953 + ... + 5430956.

Almost surely, 2^21723818 is an apocalyptic number.

21723818 is a deficient number, since it is larger than the sum of its proper divisors (10861912).

21723818 is a wasteful number, since it uses less digits than its factorization.

21723818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10861911.

The product of its digits is 5376, while the sum is 32.

The square root of 21723818 is about 4660.8816762497. The cubic root of 21723818 is about 279.0264574114.

The spelling of 21723818 in words is "twenty-one million, seven hundred twenty-three thousand, eight hundred eighteen".