21723021 has 12 divisors (see below), whose sum is σ = 31418140. Its totient is φ = 14463360.

The previous prime is 21723019. The next prime is 21723029. The reversal of 21723021 is 12032712.

It can be written as a sum of positive squares in 2 ways, for example, as 10634121 + 11088900 = 3261^2 + 3330^2 .

It is not a de Polignac number, because 21723021 - 2¹ = 21723019 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a plaindrome in base 13.

It is a junction number, because it is equal to n+sod(n) for n = 21722985 and 21723003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21723029) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 12591 + ... + 14211.

Almost surely, 2^21723021 is an apocalyptic number.

It is an amenable number.

21723021 is a deficient number, since it is larger than the sum of its proper divisors (9695119).

21723021 is a wasteful number, since it uses less digits than its factorization.

21723021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3116 (or 3113 counting only the distinct ones).

The product of its (nonzero) digits is 168, while the sum is 18.

The square root of 21723021 is about 4660.7961766205. The cubic root of 21723021 is about 279.0230450768.

Adding to 21723021 its reverse (12032712), we get a palindrome (33755733).

The spelling of 21723021 in words is "twenty-one million, seven hundred twenty-three thousand, twenty-one".