21723909 has 8 divisors (see below), whose sum is σ = 30669120. Its totient is φ = 13630656.

The previous prime is 21723907. The next prime is 21723913. The reversal of 21723909 is 90932712.

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

It is not a de Polignac number, because 21723909 - 2¹ = 21723907 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21723909.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21723907) 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 7 ways as a sum of consecutive naturals, for example, 212929 + ... + 213030.

It is an arithmetic number, because the mean of its divisors is an integer number (3833640).

Almost surely, 2^21723909 is an apocalyptic number.

It is an amenable number.

21723909 is a deficient number, since it is larger than the sum of its proper divisors (8945211).

21723909 is a wasteful number, since it uses less digits than its factorization.

21723909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 425979.

The product of its (nonzero) digits is 6804, while the sum is 33.

The square root of 21723909 is about 4660.8914383410. The cubic root of 21723909 is about 279.0268470202.

The spelling of 21723909 in words is "twenty-one million, seven hundred twenty-three thousand, nine hundred nine".