23720021 has 4 divisors (see below), whose sum is σ = 25544652. Its totient is φ = 21895392.

The previous prime is 23720003. The next prime is 23720023. The reversal of 23720021 is 12002732.

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

It can be written as a sum of positive squares in 2 ways, for example, as 2283121 + 21436900 = 1511^2 + 4630^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-23720021 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (23720023) 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 3 ways as a sum of consecutive naturals, for example, 912296 + ... + 912321.

It is an arithmetic number, because the mean of its divisors is an integer number (6386163).

Almost surely, 2^23720021 is an apocalyptic number.

It is an amenable number.

23720021 is a deficient number, since it is larger than the sum of its proper divisors (1824631).

23720021 is a wasteful number, since it uses less digits than its factorization.

23720021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1824630.

The product of its (nonzero) digits is 168, while the sum is 17.

The square root of 23720021 is about 4870.3204206705. The cubic root of 23720021 is about 287.3238583315.

Adding to 23720021 its reverse (12002732), we get a palindrome (35722753).

The spelling of 23720021 in words is "twenty-three million, seven hundred twenty thousand, twenty-one".